Bulk acoustic wave (BAW) resonator structures, devices, and systems

ABSTRACT

Techniques for improving Bulk Acoustic Wave (BAW) resonator structures are disclosed, including filters, oscillators and systems that may include such devices. First and second layers of piezoelectric material may be acoustically coupled with one another to have a piezoelectrically excitable resonance mode. The first layer of piezoelectric material may have a first piezoelectric axis orientation, and the second layer of piezoelectric material may have a second piezoelectric axis orientation that opposes the first piezoelectric axis orientation of the first layer of piezoelectric material. A top acoustic reflector including a first pair of top metal electrode layers may be electrically and acoustically coupled with the first layer of piezoelectric material to excite the piezoelectrically excitable main resonance mode at a resonant frequency.

PRIORITY CLAIM

This application is a continuation of PCT Application No.PCTUS2020043716 filed Jul. 27, 2020, titled “BULK ACOUSTIC WAVE (BAW)RESONATOR STRUCTURES, DEVICES AND SYSTEMS”, which claims priority to thefollowing provisional patent applications:

-   U.S. Provisional Patent Application Ser. No. 62/881,061, entitled    “BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES AND SYSTEMS”    and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,074, entitled    “ACOUSTIC DEVICE STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul.    31, 2019; U.S. Provisional Patent Application Ser. No. 62/881,077,    entitled “DOPED BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES,    DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,085, entitled    “BULK ACOUSTIC WAVE (BAW) RESONATOR WITH PATTERNED LAYER STRUCTURES,    DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,087, entitled    “BULK ACOUSTIC WAVE (BAW) REFLECTOR AND RESONATOR STRUCTURES,    DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,091, entitled    “MASS LOADED BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES    AND SYSTEMS” and filed on Jul. 31, 2019; and-   U.S. Provisional Patent Application Ser. No. 62/881,094, entitled    “TEMPERATURE COMPENSATING BULK ACOUSTIC WAVE (BAW) RESONATOR    STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul. 31, 2019.-   This patent is also a continuation of U.S. patent application Ser.    No. 17/380,011 filed Jul. 20, 2021, entitled “STRUCTURES, ACOUSTIC    WAVE RESONATORS, DEVICES AND SYSTEMS TO SENSE A TARGET VARIABLE”,    which in turn is a continuation of U.S. patent application Ser. No.    16/940,172 filed Jul. 27, 2020 (issued as U.S. Pat. No. 11,101,783    on Aug. 24, 2021), entitled “STRUCTURES, ACOUSTIC WAVE RESONATORS,    DEVICES AND SYSTEMS TO SENSE A TARGET VARIABLE, INCLUDING AS A    NON-LIMITING EXAMPLE CORONAVIRUSES”, which in turn claims priority    to the U.S. Provisional patent applications:-   U.S. Provisional Patent Application Ser. No. 62/881,061, entitled    “BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES AND SYSTEMS”    and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,074, entitled    “ACOUSTIC DEVICE STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul.    31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,077, entitled    “DOPED BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES AND    SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,085, entitled    “BULK ACOUSTIC WAVE (BAW) RESONATOR WITH PATTERNED LAYER STRUCTURES,    DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,087, entitled    “BULK ACOUSTIC WAVE (BAW) REFLECTOR AND RESONATOR STRUCTURES,    DEVICES AND SYSTEMS” and filed on Jul. 31, 2019;-   U.S. Provisional Patent Application Ser. No. 62/881,091, entitled    “MASS LOADED BULK ACOUSTIC WAVE (BAW) RESONATOR STRUCTURES, DEVICES    AND SYSTEMS” and filed on Jul. 31, 2019; and-   U.S. Provisional Patent Application Ser. No. 62/881,094, entitled    “TEMPERATURE COMPENSATING BULK ACOUSTIC WAVE (BAW) RESONATOR    STRUCTURES, DEVICES AND SYSTEMS” and filed on Jul. 31, 2019.

Each of the applications identified above are hereby incorporated byreference in their entirety.

TECHNICAL FIELD

The present disclosure relates to acoustic resonators and to devices andto systems comprising acoustic resonators.

BACKGROUND

Bulk Acoustic Wave (BAW) resonators have enjoyed commercial success infilter applications. For example, 4G cellular phones that operate onfourth generation broadband cellular networks typically include a largenumber of BAW filters for various different frequency bands of the 4Gnetwork. In addition to BAW resonators and filters, also included in 4Gphones are filters using Surface Acoustic Wave (SAW) resonators,typically for lower frequency band filters. SAW based resonators andfilters are generally easier to fabricate than BAW based filters andresonators. However, performance of SAW based resonators and filters maydecline if attempts are made to use them for higher 4G frequency bands.Accordingly, even though BAW based filters and resonators are relativelymore difficult to fabricate than SAW based filters and resonators, theycan be included in 4G cellular phones to provide better performance inhigher 4G frequency bands what is provided by SAW based filters andresonators.

5G cellular phones can operate on newer, fifth generation broadbandcellular networks. 5G frequencies include some frequencies that are muchhigher frequency than 4G frequencies. Such relatively higher 5Gfrequencies can transport data at relatively faster speeds than what canbe provided over relatively lower 4G frequencies. However, previouslyknown SAW and BAW based resonators and filters have encounteredperformance problems when attempts were made to use them at relativelyhigher 5G frequencies. Many learned engineering scholars have studiedthese problems, but have not found solutions. For example, performanceproblems cited for previously known SAW and BAW based resonators andfilters include scaling issues and significant increases in acousticlosses at high frequencies.

From the above, it is seen that techniques for improving acoustic devicestructures are highly desirable, for example for operation overfrequencies higher than 4G frequencies, in particular for filters,oscillators and systems that can include such devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram that illustrates an example bulk acoustic waveresonator structure.

FIG. 1B is a simplified view of FIG. 1A that illustrates acoustic stressprofile during electrical operation of the bulk acoustic wave resonatorstructure shown in FIG. 1A.

FIG. 1C shows a simplified top plan view of a bulk acoustic waveresonator structure corresponding to the cross sectional view of FIG.1A, and also shows another simplified top plan view of an alternativebulk acoustic wave resonator structure.

FIG. 1D is a perspective view of an illustrative model of a crystalstructure of MN in piezoelectric material of layers in FIG. 1A havingreverse axis orientation of negative polarization.

FIG. 1E is a perspective view of an illustrative model of a crystalstructure of MN in piezoelectric material of layers in FIG. 1A havingnormal axis orientation of positive polarization.

FIGS. 2A and 2B show a further simplified view of a bulk acoustic waveresonator similar to the bulk acoustic wave resonator structure shown inFIG. 1A along with its corresponding impedance versus frequency responseduring its electrical operation, as well as alternative bulk acousticwave resonator structures with differing numbers of alternating axispiezoelectric layers, and their respective corresponding impedanceversus frequency response during electrical operation, as predicted bysimulation.

FIG. 2C shows additional alternative bulk acoustic wave resonatorstructures with additional numbers of alternating axis piezoelectriclayers.

FIGS. 2D and 2E show more additional alternative bulk acoustic waveresonator structures.

FIGS. 3A through 3E illustrate example integrated circuit structuresused to form the example bulk acoustic wave resonator structure of FIG.1A. Note that although AlN is used as an example piezoelectric layermaterial, the present disclosure is not intended to be so limited. Forexample, in some embodiments, the piezoelectric layer material mayinclude other group III material-nitride (III-N) compounds (e.g., anycombination of one or more of gallium, indium, and aluminum withnitrogen), and further, any of the foregoing may include doping, forexample, of Scandium and/or Magnesium doping.

FIGS. 4A through 4G show alternative example bulk acoustic waveresonators to the example bulk acoustic wave resonator structures shownin FIG. 1A.

FIG. 5 shows a schematic of an example ladder filter using three seriesresonators of the bulk acoustic wave resonator structure of FIG. 1A, andtwo mass loaded shunt resonators of the bulk acoustic wave resonatorstructure of FIG. 1A, along with a simplified view of the three seriesresonators.

FIG. 6 shows a schematic of an example ladder filter using five seriesresonators of the bulk acoustic wave resonator structure of FIG. 1A, andfour mass loaded shunt resonators of the bulk acoustic wave resonatorstructure of FIG. 1A, along with a simplified top view of the nineresonators interconnected in the example ladder filter, and lateraldimensions of the example ladder filter.

FIG. 7 shows an schematic of example inductors modifying an examplelattice filter using a first pair of series resonators of the bulkacoustic wave resonator structure of FIG. 1A, a second pair of seriesresonators of the bulk acoustic wave resonator structure of FIG. 1A andtwo pairs of cross coupled mass loaded shunt resonators of the bulkacoustic wave resonator structure of FIG. 1A.

FIG. 8A shows an example oscillator using the bulk acoustic waveresonator structure of FIG. 1A.

FIG. 8B shows a schematic of and example circuit implementation of theoscillator shown in FIG. 8A.

FIGS. 9A and 9B are simplified diagrams of a frequency spectrumillustrating application frequencies and application frequency bands ofthe example bulk acoustic wave resonators shown in FIG. 1A and FIGS. 4Athrough 4G, and the example filters shown in FIGS. 5 through 7 , and theexample oscillators shown in FIGS. 8A and 8B.

FIGS. 9C and 9D are diagrams illustrating respective simulated bandpasscharacteristics of insertion loss versus frequency for examplemillimeter wave filters.

FIG. 10 illustrates a computing system implemented with integratedcircuit structures or devices formed using the techniques disclosedherein, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

Non-limiting embodiments will be described by way of example withreference to the accompanying figures, which are schematic and are notintended to be drawn to scale. In the figures, each identical or nearlyidentical component illustrated is typically represented by a singlenumeral. For purposes of clarity, not every component is labeled inevery figure, nor is every component of each embodiment shown whereillustration is not necessary to allow understanding by those ofordinary skill in the art. In the specification, as well as in theclaims, all transitional phrases such as “comprising,” “including,”“carrying,” “having,” “containing,” “involving,” “holding,” “composedof,” and the like are to be understood to be open-ended, i.e., to meanincluding but not limited to. Only the transitional phrases “consistingof” and “consisting essentially of” shall be closed or semi-closedtransitional phrases, respectively. Further, relative terms, such as“above,” “below,” “top,” “bottom,” “upper” and “lower” are used todescribe the various elements' relationships to one another, asillustrated in the accompanying drawings. It is understood that theserelative terms are intended to encompass different orientations of thedevice and/or elements in addition to the orientation depicted in thedrawings. For example, if the device were inverted with respect to theview in the drawings, an element described as “above” another element,for example, would now be below that element. The term “compensating” isto be understood as including “substantially compensating”. The terms“oppose”, “opposes” and “opposing” are to be understood as including“substantially oppose”, “substantially opposes” and “substantiallyopposing” respectively. Further, as used in the specification andappended claims, and in addition to their ordinary meanings, the terms“substantial” or “substantially” mean to within acceptable limits ordegree. For example, “substantially cancelled” means that one skilled inthe art would consider the cancellation to be acceptable. As used in thespecification and the appended claims and in addition to its ordinarymeaning, the term “approximately” or “about” means to within anacceptable limit or amount to one of ordinary skill in the art. Forexample, “approximately the same” means that one of ordinary skill inthe art would consider the items being compared to be the same. As usedin the specification and appended claims, the terms “a”, “an” and “the”include both singular and plural referents, unless the context clearlydictates otherwise. Thus, for example, “a device” includes one deviceand plural devices. As used herein, the International TelecommunicationUnion (ITU) defines Super High Frequency (SHF) as extending betweenthree Gigahertz (3 GHz) and thirty Gigahertz (30 GHz). The ITU definesExtremely High Frequency (EHF) as extending between thirty Gigahertz (30GHz) and three hundred Gigahertz (300 GHz).

FIG. 1A is a diagram that illustrates an example bulk acoustic waveresonator structure 100. FIGS. 4A through 4G show alternative examplebulk acoustic wave resonators, 400A through 400G, to the example bulkacoustic wave resonator structure 100 shown in FIG. 1A. The foregoingare shown in simplified cross sectional views. The resonator structuresare formed over a substrate 101, 401A through 401G (e.g., siliconsubstrate 101, 401A, 401B, 401D through 401F, e.g., silicon carbidesubstrate 401C. In some examples, the substrate may further comprise aseed layer 103, 403A, 403B, 403D through 403F, formed of, for example,aluminum nitride (AlN), or another suitable material (e.g., silicondioxide (SiO₂), aluminum oxide (Al₂O₃), silicon nitride (Si₃N₄),amorphous silicon (a-Si), silicon carbide (SiC)), having an examplethickness in a range from approximately 100 A to approximately 1 um onthe silicon substrate.

The example resonators 100, 400A through 400G, include a respectivestack 104, 404A through 404G, of an example four layers of piezoelectricmaterial, for example, four layers of Aluminum Nitride (AlN) having awurtzite structure. For example, FIG. 1A and FIGS. 4A through 4G show abottom piezoelectric layer 105, 405A through 405G, a first middlepiezoelectric layer 107, 407A through 407G, a second middlepiezoelectric layer 109, 409A through 409G, and a top piezoelectriclayer 111, 411A through 411G. A mesa structure 104, 404A through 404G(e.g., first mesa structure 104, 404A through 404G) may comprise therespective stack 104, 404A through 404G, of the example four layers ofpiezoelectric material. The mesa structure 104, 404A through 404G (e.g.,first mesa structure 104, 404A through 404G) may comprise bottompiezoelectric layer 105, 405A through 405G. The mesa structure 104, 404Athrough 404G (e.g., first mesa structure 104, 404A through 404G) maycomprise first middle piezoelectric layer 107, 407A through 407G. Themesa structure 104, 404A through 404G (e.g., first mesa structure 104,404A through 404G) may comprise second middle piezoelectric layer 109,409A through 409G. The mesa structure 104, 404A through 404G (e.g.,first mesa structure 104, 404A through 404G) may comprise toppiezoelectric layer 111, 411A through 411G.

The four layers of piezoelectric material in the respective stack 104,404A through 404G of FIG. 1A and FIGS. 4A through 4G may have analternating axis arrangement in the respective stack 104, 404A through404G. For example the bottom piezoelectric layer 105, 405A through 405Gmay have a normal axis orientation, which is depicted in the figuresusing a downward directed arrow. Next in the alternating axisarrangement of the respective stack 104, 404A through 404G, the firstmiddle piezoelectric layer 107, 407A through 407G may have a reverseaxis orientation, which is depicted in the figures using an upwarddirected arrow. Next in the alternating axis arrangement of therespective stack 104, 404A through 404G, the second middle piezoelectriclayer 109, 409A through 409G may have the normal axis orientation, whichis depicted in the figures using the downward directed arrow. Next inthe alternating axis arrangement of the respective stack 104, 404Athrough 404G, the top piezoelectric layer 111, 411A through 411G mayhave the reverse axis orientation, which is depicted in the figuresusing the upward directed arrow.

For example, polycrystalline thin film MN may be grown in acrystallographic c-axis negative polarization, or normal axisorientation perpendicular relative to the substrate surface usingreactive magnetron sputtering of an Aluminum target in a nitrogenatmosphere. However, as will be discussed in greater detail subsequentlyherein, changing sputtering conditions, for example by adding oxygen,may reverse the axis to a crystallographic c-axis positive polarization,or reverse axis, orientation perpendicular relative to the substratesurface.

In the example resonators 100, 400A through 400G, of FIG. 1A and FIGS.4A through 4G, the bottom piezoelectric layer 105, 405A through 405G,may have a piezoelectrically excitable resonance mode (e.g., mainresonance mode) at a resonant frequency (e.g., main resonant frequency)of the example resonators. Similarly, the first middle piezoelectriclayer 107, 407A through 407G, may have its piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the example resonators. Similarly,the second middle piezoelectric layer 109, 409A through 409G, may haveits piezoelectrically excitable resonance mode (e.g., main resonancemode) at the resonant frequency (e.g., main resonant frequency) of theexample resonators. Similarly, the top piezoelectric layer 111, 411Athrough 411G, may have its piezoelectrically excitable main resonancemode (e.g., main resonance mode) at the resonant frequency (e.g., mainresonant frequency) of the example resonators. Accordingly, the toppiezoelectric layer 111, 411A through 411G, may have itspiezoelectrically excitable main resonance mode (e.g., main resonancemode) at the resonant frequency (e.g., main resonant frequency) with thebottom piezoelectric layer 105, 405A through 405G, the first middlepiezoelectric layer 107, 407A through 407G, and the second middlepiezoelectric layer 109, 409A through 409G.

The bottom piezoelectric layer 105, 405A through 405G, may beacoustically coupled with the first middle piezoelectric layer 107, 407Athrough 407G, in the piezoelectrically excitable resonance mode (e.g.,main resonance mode) at the resonant frequency (e.g., main resonantfrequency) of the example resonators 100, 400A through 400G. The normalaxis of bottom piezoelectric layer 105, 405A through 405G, in opposingthe reverse axis of the first middle piezoelectric layer 107, 407Athrough 407G, may cooperate for the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the example resonators. The firstmiddle piezoelectric layer 107, 407A through 407G, may be sandwichedbetween the bottom piezoelectric layer 105, 405A through 405G, and thesecond middle piezoelectric layer 109, 409A through 409G, for example,in the alternating axis arrangement in the respective stack 104, 404Athrough 404G. For example, the reverse axis of the first middlepiezoelectric layer 107, 407A through 407G, may oppose the normal axisof the bottom piezoelectric layer 105, 405A through 405G, and the normalaxis of the second middle piezoelectric layer 109, 409A-409G. Inopposing the normal axis of the bottom piezoelectric layer 105, 405Athrough 405G, and the normal axis of the second middle piezoelectriclayer 109, 409A through 409G, the reverse axis of the first middlepiezoelectric layer 107, 407A through 407G, may cooperate for thepiezoelectrically excitable resonance mode (e.g., main resonance mode)at the resonant frequency (e.g., main resonant frequency) of the exampleresonators.

The second middle piezoelectric layer 109, 409A through 409G, may besandwiched between the first middle piezoelectric layer 107, 407Athrough 407G, and the top piezoelectric layer 111, 411A through 411G,for example, in the alternating axis arrangement in the respective stack104, 404A through 404G. For example, the normal axis of the secondmiddle piezoelectric layer 109, 409A through 409G, may oppose thereverse axis of the first middle piezoelectric layer 107, 407A through407G, and the reverse axis of the top piezoelectric layer 111, 411Athrough 411G. In opposing the reverse axis of the first middlepiezoelectric layer 107, 407A through 407G, and the reverse axis of thetop piezoelectric layer 111, 411A through 411G, the normal axis of thesecond middle piezoelectric layer 109, 409A through 409G, may cooperatefor the piezoelectrically excitable resonance mode (e.g., main resonancemode) at the resonant frequency (e.g., main resonant frequency) of theexample resonators. Similarly, the alternating axis arrangement of thebottom piezoelectric layer 105, 405A through 405G, and the first middlepiezoelectric layer 107, 407A through 407G, and the second middlepiezoelectric layer 109, 409A through 409G, and the top piezoelectriclayer 111, 411A-411G, in the respective stack 104, 404A through 404G maycooperate for the piezoelectrically excitable resonance mode (e.g., mainresonance mode) at the resonant frequency (e.g., main resonantfrequency) of the example resonators. Despite differing in theiralternating axis arrangement in the respective stack 104, 404A through404G, the bottom piezoelectric layer 105, 405A through 405G and thefirst middle piezoelectric layer 107, 407A through 407G, and the secondmiddle piezoelectric layer 109, 409A through 409G, and the toppiezoelectric layer 111, 411A through 411G, may all be made of the samepiezoelectric material, e.g., Aluminum Nitride (AlN).

Respective layers of piezoelectric material in the stack 104, 404Athrough 404G, of FIG. 1A and FIGS. 4A through 4G may have respectivelayer thicknesses of about one half wavelength (e.g., about one halfacoustic wavelength) of the main resonant frequency of the exampleresonators. For example, respective layers of piezoelectric material inthe stack 104, 404A through 404G, of FIG. 1A and FIGS. 4A through 4G mayhave respective layer thicknesses so that (e.g., selected so that) therespective bulk acoustic wave resonators 100, 400A through 400G may haverespective resonant frequencies that are in a Super High Frequency (SHF)band or an Extremely High Frequency (EHF) band (e.g., respectiveresonant frequencies that are in a Super High Frequency (SHF) band,e.g., respective resonant frequencies that are in an Extremely HighFrequency (EHF) band.) For example, respective layers of piezoelectricmaterial in the stack 104, 404A through 404G, of FIG. 1A and FIGS. 4Athrough 4G may have respective layer thicknesses so that (e.g., selectedso that) the respective bulk acoustic wave resonators 100, 400A through400G may have respective resonant frequencies that are in a millimeterwave band. For example, for a twenty-four gigahertz (e.g., 24 GHz) mainresonant frequency of the example resonators, the bottom piezoelectriclayer 105, 405A through 405G, may have a layer thickness correspondingto about one half of a wavelength (e.g., about one half of an acousticwavelength) of the main resonant frequency, and may be about twothousand Angstroms (2000 A). Similarly, the first middle piezoelectriclayer 107, 407A through 407G, may have a layer thickness correspondingthe one half of the wavelength (e.g., one half of the acousticwavelength) of the main resonant frequency; the second middlepiezoelectric layer 109, 409A through 409G, may have a layer thicknesscorresponding the one half of the wavelength (e.g., one half of theacoustic wavelength) of the main resonant frequency; and the toppiezoelectric layer 111, 411A through 411G, may have a layer thicknesscorresponding the one half of the wavelength (e.g., one half of theacoustic wavelength) of the main resonant frequency. Piezoelectric layerthickness may be scaled up or down to determine main resonant frequency.

The example resonators 100, 400A through 400G, of FIG. 1A and FIGS. 4Athrough 4G may comprise: a bottom acoustic reflector 113, 413A through413G, including an acoustically reflective bottom electrode stack of aplurality of bottom metal electrode layers; and a top acoustic reflector115, 415A through 415G, including an acoustically reflective bottomelectrode stack of a plurality of top metal electrode layers.Accordingly, the bottom acoustic reflector 113, 413A through 413G, maybe a bottom multilayer acoustic reflector, and the top acousticreflector 115, 415A through 415G, may be a top multilayer acousticreflector. The piezoelectric layer stack 104, 404A through 404G, may besandwiched between the plurality of bottom metal electrode layers of thebottom acoustic reflector 113, 413A through 413G, and the plurality oftop metal electrode layers of the top acoustic reflector 115, 415Athrough 415G. For example, top acoustic reflector electrode 115, 415Athrough 415G and bottom acoustic reflector electrode 113, 413A through413G may abut opposite sides of a resonant volume 104, 404A through 404G(e.g., piezoelectric layer stack 104, 404A through 404G) free of anyinterposing electrode. The piezoelectric layer stack 104, 404A through404G, may be electrically and acoustically coupled with the plurality ofbottom metal electrode layers of the bottom acoustic reflector 113, 413Athrough 413G and the plurality of top metal electrode layers of the topacoustic reflector 115, 415A through 415G, to excite thepiezoelectrically excitable resonance mode (e.g., main resonance mode)at the resonant frequency (e.g., main resonant frequency). For example,such excitation may be done by using the plurality of bottom metalelectrode layers of the bottom acoustic reflector 113, 413A through 413Gand the plurality of top metal electrode layers of the top acousticreflector 115, 415A through 415G to apply an oscillating electric fieldhaving a frequency corresponding to the resonant frequency (e.g., mainresonant frequency) of the piezoelectric layer stack 104, 404A through404G, and of the example resonators 100, 400A through 400G. For example,the piezoelectric layer stack 104, 404A through 404G, may beelectrically and acoustically coupled with the plurality of bottom metalelectrode layers of the bottom acoustic reflector 113, 413A through 413Gand the plurality of top metal electrode layers of the top acousticreflector 115, 415A through 415G, to excite the piezoelectricallyexcitable resonance mode (e.g., main resonance mode) at the resonantfrequency (e.g., main resonant frequency).

For example, the bottom piezoelectric layer 105, 405A through 405G, maybe electrically and acoustically coupled with the plurality of bottommetal electrode layers of the bottom acoustic reflector 113, 413Athrough 413G and the plurality of top metal electrode layers of the topacoustic reflector 115, 415A through 415G, to excite thepiezoelectrically excitable resonance mode (e.g., main resonance mode)at the resonant frequency (e.g., main resonant frequency) of the bottompiezoelectric layer 105, 405A through 405G. Further, the bottompiezoelectric layer 105, 405A through 405G and the first middlepiezoelectric layer 107, 407A through 407G, may be electrically andacoustically coupled with the plurality of bottom metal electrode layersof the bottom acoustic reflector 113, 413A through 413G, and theplurality of top metal electrode layers of the top acoustic reflector115, 415A through 415G, to excite the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the bottom piezoelectric layer 105,405A through 405G, acoustically coupled with the first middlepiezoelectric layer 107, 407A through 407G. Additionally, the firstmiddle piezoelectric layer 107, 407A-407G, may be sandwiched between thebottom piezoelectric layer 105, 405A through 405G and the second middlepiezoelectric layer 109, 409A through 409G, and may be electrically andacoustically coupled with the plurality of bottom metal electrode layersof the bottom acoustic reflector 113, 413A through 413G, and theplurality of top metal electrode layers of the top acoustic reflector115, 415A through 415G, to excite the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the first middle piezoelectric layer107, 407A through 407G, sandwiched between the bottom piezoelectriclayer 105, 405A through 405G, and the second middle piezoelectric layer109, 409A through 409G.

The acoustically reflective bottom electrode stack of the plurality ofbottom metal electrode layers of the bottom acoustic reflector 113, 413Athrough 413G, may have an alternating arrangement of low acousticimpedance metal layer and high acoustic impedance metal layer. Forexample, an initial bottom metal electrode layer 117, 417A through 417G,may comprise a relatively high acoustic impedance metal, for example,Tungsten having an acoustic impedance of about 100 MegaRayls, or forexample, Molybdenum having an acoustic impedance of about 65 MegaRayls.The acoustically reflective bottom electrode stack of the plurality ofbottom metal electrode layers of the bottom acoustic reflector 113, 413Athrough 413G may approximate a metal distributed Bragg acousticreflector. The plurality of metal bottom electrode layers of the bottomacoustic reflector may be electrically coupled (e.g., electricallyinterconnected) with one another. The acoustically reflective bottomelectrode stack of the plurality of bottom metal electrode layers mayoperate together as a multilayer (e.g., bilayer, e.g., multiple layer)bottom electrode for the bottom acoustic reflector 113, 413A through413G.

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective bottom electrode stack, may be a first pair of bottom metalelectrode layers 119, 419A through 419G and 121, 421A through 421G. Afirst member 119, 419A through 419G, of the first pair of bottom metalelectrode layers may comprise a relatively low acoustic impedance metal,for example, Titanium having an acoustic impedance of about 27MegaRayls, or for example, Aluminum having an acoustic impedance ofabout 18 MegaRayls. A second member 121, 421A through 421G, of the firstpair of bottom metal electrode layers may comprise the relatively highacoustic impedance metal, for example, Tungsten or Molybdenum.Accordingly, the first pair of bottom metal electrode layers 119, 419Athrough 419G, and 121, 421A through 421G, of the bottom acousticreflector 113, 413A through 413G, may be different metals, and may haverespective acoustic impedances that are different from one another so asto provide a reflective acoustic impedance mismatch at the resonantfrequency (e.g., main resonant frequency). Similarly, the initial bottommetal electrode layer 117, 417A through 417G, and the first member ofthe first pair of bottom metal electrode layers 119, 419A through 419G,of the bottom acoustic reflector 113, 413A through 413G, may bedifferent metals, and may have respective acoustic impedances that aredifferent from one another so as to provide a reflective acousticimpedance mismatch at the resonant frequency (e.g., main resonantfrequency).

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective bottom electrode stack, a second pair of bottom metalelectrode layers 123, 423A through 423G, and 125, 425A through 425G, mayrespectively comprise the relatively low acoustic impedance metal andthe relatively high acoustic impedance metal. Accordingly, the initialbottom metal electrode layer 117, 417A through 417G, and members of thefirst and second pairs of bottom metal electrode layers 119, 419Athrough 419G, 121, 421A through 421G, 123, 423A through 423G, 125, 425Athrough 425G, may have respective acoustic impedances in the alternatingarrangement to provide a corresponding plurality of reflective acousticimpedance mismatches.

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective bottom electrode stack, a third pair of bottom metalelectrode layers 127, 427D, 129, 429D may respectively comprise therelatively low acoustic impedance metal and the relatively high acousticimpedance metal. Next in the alternating arrangement of low acousticimpedance metal layer and high acoustic impedance metal layer of theacoustically reflective bottom electrode stack, a fourth pair of bottommetal electrode layers 131, 431D and 133, 433D may respectively comprisethe relatively low acoustic impedance metal and the relatively highacoustic impedance metal.

Respective thicknesses of the bottom metal electrode layers may berelated to wavelength (e.g., acoustic wavelength) for the main resonantfrequency of the example bulk acoustic wave resonators, 100, 400Athrough 400G. Further, various embodiments for resonators havingrelatively higher resonant frequency (higher main resonant frequency)may have relatively thinner bottom metal electrode thicknesses, e.g.,scaled thinner with relatively higher resonant frequency (e.g., highermain resonant frequency). Similarly, various alternative embodiments forresonators having relatively lower resonant frequency (e.g., lower mainresonant frequency) may have relatively thicker bottom metal electrodelayer thicknesses, e.g., scaled thicker with relatively lower resonantfrequency (e.g., lower main resonant frequency). For example, a layerthickness of the initial bottom metal electrode layer 117, 417A through417G, may be about one eighth of a wavelength (e.g., one eighth of anacoustic wavelength) at the main resonant frequency of the exampleresonator. For example, if molybdenum is used as the high acousticimpedance metal and the main resonant frequency of the resonator istwenty-four gigahertz (e.g., 24 GHz), then using the one eighth of thewavelength (e.g., one eighth of the acoustic wavelength) provides thelayer thickness of the initial bottom metal electrode layer 117, 417Athrough 417G, as about three hundred and thirty Angstroms (330 A). Inthe foregoing example, the one eighth of the wavelength (e.g., the oneeighth of the acoustic wavelength) at the main resonant frequency wasused for determining the layer thickness of the initial bottom metalelectrode layer 117, 417A-417G, but it should be understood that thislayer thickness may be varied to be thicker or thinner in various otheralternative example embodiments.

Respective layer thicknesses, T01 through T08, shown in FIG. 1A formembers of the pairs of bottom metal electrode layers may be about anodd multiple (e.g., 1×, 3×, etc.) of a quarter of a wavelength (e.g.,one quarter of the acoustic wavelength) at the main resonant frequencyof the example resonator. However, the foregoing may be varied. Forexample, members of the pairs of bottom metal electrode layers of thebottom acoustic reflector may have respective layer thickness thatcorrespond to from about one eighth to about one half wavelength at theresonant frequency, or an odd multiple (e.g., 1×, 3×, etc.) thereof.

In an example, if Tungsten is used as the high acoustic impedance metal,and the main resonant frequency of the resonator is twenty-fourgigahertz (e.g., 24 GHz), then using the one quarter of the wavelength(e.g., one quarter of the acoustic wavelength) provides the layerthickness of the high impedance metal electrode layer members of thepairs as about five hundred and forty Angstroms (540 A). For example, ifTitanium is used as the low acoustic impedance metal, and the mainresonant frequency of the resonator is twenty-four gigahertz (e.g., 24GHz), then using the one quarter of the wavelength (e.g., one quarter ofthe acoustic wavelength) provides the layer thickness of the lowimpedance metal electrode layer members of the pairs as about sixhundred and thirty Angstroms (630 A). Similarly, respective layerthicknesses for members of the pairs of bottom metal electrode layersshown in FIGS. 4A through 4G may likewise be about one quarter of thewavelength (e.g., one quarter of the acoustic wavelength) of the mainresonant frequency of the example resonator, and these respective layerthicknesses may likewise be determined for members of the pairs ofbottom metal electrode layers for the high and low acoustic impedancemetals employed.

For example, the bottom piezoelectric layer 105, 405A through 405G, maybe electrically and acoustically coupled with the initial bottom metalelectrode layer 117, 417A through 417G, and pair(s) of bottom metalelectrode layers (e.g., first pair of bottom metal electrode layers 119,419A through 419G, 121, 421A through 421G, e.g., second pair of bottommetal electrode layers 123, 423A through 423G, 125, 425A through 425G,e.g., third pair of bottom metal electrode layers 127, 427D, 129, 429D,fourth pair of bottom metal electrode layers 131, 431D, 133, 433D), toexcite the piezoelectrically excitable resonance mode (e.g., mainresonance mode) at the resonant frequency (e.g., main resonantfrequency) of the bottom piezoelectric layer 105, 405A through 405G.Further, the bottom piezoelectric layer 105, 405A through 405G and thefirst middle piezoelectric layer 107, 407A through 407G may beelectrically and acoustically coupled with the initial bottom metalelectrode layer 117, 417A through 417G and pair(s) of bottom metalelectrode layers (e.g., first pair of bottom metal electrode layers 119,419A through 419G, 121, 421A through 421G, e.g., second pair of bottommetal electrode layers 123, 423A through 423G, 125, 425A through 425G,e.g., third pair of bottom metal electrode layers 127, 427D, 129, 429D),to excite the piezoelectrically excitable resonance mode (e.g., mainresonance mode) at the resonant frequency (e.g., main resonantfrequency) of the bottom piezoelectric layer 105, 405A through 405Gacoustically coupled with the first middle piezoelectric layer 107, 407Athrough 407G. Additionally, the first middle piezoelectric layer 107,407A through 407G, may be sandwiched between the bottom piezoelectriclayer 105, 405A through 405G, and the second middle piezoelectric layer109, 409A through 409G, and may be electrically and acoustically coupledwith initial bottom metal electrode layer 117, 417A through 417G, andpair(s) of bottom metal electrode layers (e.g., first pair of bottommetal electrode layers 119, 419A through 419G, 121, 421A through 421G,e.g., second pair of bottom metal electrode layers 123, 423A through423G, 125, 425A through 425G, e.g., third pair of bottom metal electrodelayers 127, 427D, 129, 429D), to excite the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the first middle piezoelectric layer107, 407A through 407G, sandwiched between the bottom piezoelectriclayer 105, 405A through 405G, and the second middle piezoelectric layer109, 409A through 409G.

Another mesa structure 113, 413A through 413G, (e.g., second mesastructure 113, 413A through 413G), may comprise the bottom acousticreflector 113, 413A through 413G. The another mesa structure 113, 413Athrough 413G, (e.g., second mesa structure 113, 413A through 413G), maycomprise initial bottom metal electrode layer 117, 417A through 417G.The another mesa structure 113, 413A through 413G, (e.g., second mesastructure 113, 413A through 413G), may comprise one or more pair(s) ofbottom metal electrode layers (e.g., first pair of bottom metalelectrode layers 119, 419A through 419G, 121, 421A through 421G, e.g.,second pair of bottom metal electrode layers 123, 423A through 423G,125, 425A through 425G, e.g., third pair of bottom metal electrodelayers 127, 427A, 427D, 129, 429D, e.g., fourth pair of bottom metalelectrode layers 131, 431D, 133, 433D).

Similar to what has been discussed for the bottom electrode stack,likewise the top electrode stack of the plurality of top metal electrodelayers of the top acoustic reflector 115, 415A through 415G, may havethe alternating arrangement of low acoustic impedance metal layer andhigh acoustic impedance metal layer. For example, an initial top metalelectrode layer 135, 435A through 435G, may comprise the relatively highacoustic impedance metal, for example, Tungsten or Molybdenum. The topelectrode stack of the plurality of top metal electrode layers of thetop acoustic reflector 115, 415A through 415G, may approximate a metaldistributed Bragg acoustic reflector. The plurality of top metalelectrode layers of the top acoustic reflector may be electricallycoupled (e.g., electrically interconnected) with one another. Theacoustically reflective top electrode stack of the plurality of topmetal electrode layers may operate together as a multilayer (e.g.,bilayer, e.g., multiple layer) top electrode for the top acousticreflector 115, 415A through 415G. Next in the alternating arrangement oflow acoustic impedance metal layer and high acoustic impedance metallayer of the acoustically reflective top electrode stack, may be a firstpair of top metal electrode layers 137, 437A through 437G, and 139, 439Athrough 439G. A first member 137, 437A through 437G, of the first pairof top metal electrode layers may comprise the relatively low acousticimpedance metal, for example, Titanium or Aluminum. A second member 139,439A through 439G, of the first pair of top metal electrode layers maycomprise the relatively high acoustic impedance metal, for example,Tungsten or Molybdenum. Accordingly, the first pair of top metalelectrode layers 137, 437A through 437G, 139, 439A through 439G, of thetop acoustic reflector 115, 415A through 415G, may be different metals,and may have respective acoustic impedances that are different from oneanother so as to provide a reflective acoustic impedance mismatch at theresonant frequency (e.g., main resonant frequency). Similarly, theinitial top metal electrode layer 135, 435A through 435G, and the firstmember of the first pair of top metal electrode layers 137, 437A through437G, of the top acoustic reflector 115, 415A through 415G, may bedifferent metals, and may have respective acoustic impedances that aredifferent from one another so as to provide a reflective acousticimpedance mismatch at the resonant frequency (e.g., main resonantfrequency).

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective top electrode stack, a second pair of top metal electrodelayers 141, 441A through 441G, and 143, 443A through 443G, mayrespectively comprise the relatively low acoustic impedance metal andthe relatively high acoustic impedance metal. Accordingly, the initialtop metal electrode layer 135, 435A through 435G, and members of thefirst and second pairs of top metal electrode layers 137, 437A through437G, 139, 439A through 439G, 141, 441A through 441G, 143, 443A through443G, may have respective acoustic impedances in the alternatingarrangement to provide a corresponding plurality of reflective acousticimpedance mismatches.

Next in the alternating arrangement of low acoustic impedance metallayer and high acoustic impedance metal layer of the acousticallyreflective top electrode stack, a third pair of top metal electrodelayers 145, 445A through 445C, and 147, 447A through 447C, mayrespectively comprise the relatively low acoustic impedance metal andthe relatively high acoustic impedance metal. Next in the alternatingarrangement of low acoustic impedance metal layer and high acousticimpedance metal layer of the acoustically reflective top electrodestack, a fourth pair of top metal electrode layers 149, 449A through449C, 151, 451A through 451C, may respectively comprise the relativelylow acoustic impedance metal and the relatively high acoustic impedancemetal.

For example, the bottom piezoelectric layer 105, 405A through 405G, maybe electrically and acoustically coupled with the initial top metalelectrode layer 135, 435A through 435G, and the pair(s) of top metalelectrode layers (e.g., first pair of top metal electrode layers 137,437A through 437G, 139, 439A through 439G, e.g., second pair of topmetal electrode layers 141, 441A through 441G, 143, 443A through 443G,e.g., third pair of top metal electrode layers 145, 445A through 445C,147, 447A through 447C), to excite the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the bottom piezoelectric layer 105,405A through 405G. Further, the bottom piezoelectric layer 105, 405Athrough 405G and the first middle piezoelectric layer 107, 407A through407G may be electrically and acoustically coupled with the initial topmetal electrode layer 135, 435A through 435G and pair(s) of top metalelectrode layers (e.g., first pair of top metal electrode layers 137,437A through 437G, 139, 439A through 439G, e.g., second pair of topmetal electrode layers 141, 441A through 441G, 143, 443A through 443G,e.g., third pair of top metal electrode layers 145, 445A through 445C,147, 447A through 447C), to excite the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the bottom piezoelectric layer 105,405A through 405G acoustically coupled with the first middlepiezoelectric layer 107, 407A through 407G. Additionally, the firstmiddle piezoelectric layer 107, 407A through 407G, may be sandwichedbetween the bottom piezoelectric layer 105, 405A through 405G, and thesecond middle piezoelectric layer 109, 409A through 409G, and may beelectrically and acoustically coupled with the initial top metalelectrode layer 135, 435A through 435G, and the pair(s) of top metalelectrode layers (e.g., first pair of top metal electrode layers 137,437A through 437G, 139, 439A through 439G, e.g., second pair of topmetal electrode layers 141, 441A through 441G, 143, 443A through 443G,e.g., third pair of top metal electrode layers 145, 445A through 445C,147, 447A through 447C), to excite the piezoelectrically excitableresonance mode (e.g., main resonance mode) at the resonant frequency(e.g., main resonant frequency) of the first middle piezoelectric layer107, 407A through 407G, sandwiched between the bottom piezoelectriclayer 105, 405A through 405G, and the second middle piezoelectric layer109, 409A through 409G.

Yet another mesa structure 115, 415A through 415G, (e.g., third mesastructure 115, 415A through 415G), may comprise the top acousticreflector 115, 415A through 415G, or a portion of the top acousticreflector 115, 415A through 415G. The yet another mesa structure 115,415A through 415G, (e.g., third mesa structure 115, 415A through 415G),may comprise initial top metal electrode layer 135, 435A through 435G.The yet another mesa structure 115, 415A through 415C, (e.g., third mesastructure 115, 415A through 415C), may comprise one or more pair(s) oftop metal electrode layers (e.g., first pair of top metal electrodelayers 137, 437A through 437C, 139, 439A through 439C, e.g., second pairof top metal electrode layers 141, 441A through 441C, 143, 443A through443C, e.g., third pair of top metal electrode layers 145, 445A through445C, 147, 447A through 447C, e.g., fourth pair of top metal electrodelayers 149, 449A through 449C, 151, 451A through 451C).

Like the respective layer thicknesses of the bottom metal electrodelayers, respective thicknesses of the top metal electrode layers maylikewise be related to wavelength (e.g., acoustic wavelength) for themain resonant frequency of the example bulk acoustic wave resonators,100, 400A through 400G. Further, various embodiments for resonatorshaving relatively higher main resonant frequency may have relativelythinner top metal electrode thicknesses, e.g., scaled thinner withrelatively higher main resonant frequency. Similarly, variousalternative embodiments for resonators having relatively lower mainresonant frequency may have relatively thicker top metal electrode layerthicknesses, e.g., scaled thicker with relatively lower main resonantfrequency. Like the layer thickness of the initial bottom metal, a layerthickness of the initial top metal electrode layer 135, 435A through435G, may likewise be about one eighth of the wavelength (e.g., oneeighth of the acoustic wavelength) of the main resonant frequency of theexample resonator. For example, if molybdenum is used as the highacoustic impedance metal and the main resonant frequency of theresonator is twenty-four gigahertz (e.g., 24 GHz), then using the oneeighth of the wavelength (e.g., one eighth of the acoustic wavelength)provides the layer thickness of the initial top metal electrode layer135, 435A through 435G, as about three hundred and thirty Angstroms (330A). In the foregoing example, the one eighth of the wavelength (e.g.,one eighth of the acoustic wavelength) at the main resonant frequencywas used for determining the layer thickness of the initial top metalelectrode layer 135, 435A-435G, but it should be understood that thislayer thickness may be varied to be thicker or thinner in various otheralternative example embodiments. Respective layer thicknesses, T11through T18, shown in FIG. 1A for members of the pairs of top metalelectrode layers may be about an odd multiple (e.g., 1×, 3×, etc.) of aquarter of a wavelength (e.g., one quarter of an acoustic wavelength) ofthe main resonant frequency of the example resonator. Similarly,respective layer thicknesses for members of the pairs of top metalelectrode layers shown in FIGS. 4A through 4G may likewise be about onequarter of a wavelength (e.g., one quarter of an acoustic wavelength) atthe main resonant frequency of the example resonator multiplied by anodd multiplier (e.g., 1×, 3×, etc.), and these respective layerthicknesses may likewise be determined for members of the pairs of topmetal electrode layers for the high and low acoustic impedance metalsemployed. However, the foregoing may be varied. For example, members ofthe pairs of top metal electrode layers of the top acoustic reflectormay have respective layer thickness that correspond to from an oddmultiple (e.g., 1×, 3×, etc.) of about one eighth to an odd multiple(e.g., 1×, 3×, etc.) of about one half wavelength at the resonantfrequency.

The bottom acoustic reflector 113, 413A through 413G, may have athickness dimension T23 extending along the stack of bottom electrodelayers. For the example of the 24 GHz resonator, the thickness dimensionT23 of the bottom acoustic reflector may be about five thousandAngstroms (5,000 A). The top acoustic reflector 115, 415A through 415G,may have a thickness dimension T25 extending along the stack of topelectrode layers. For the example of the 24 GHz resonator, the thicknessdimension T25 of the top acoustic reflector may be about five thousandAngstroms (5,000 A). The piezoelectric layer stack 104, 404A through404G, may have a thickness dimension T27 extending along thepiezoelectric layer stack 104, 404A through 404G. For the example of the24 GHz resonator, the thickness dimension T27 of the piezoelectric layerstack may be about eight thousand Angstroms (8,000 A).

In the example resonators 100, 400A through 400G, of FIG. 1A and FIGS.4A through 4G, a notional heavy dashed line is used in depicting anetched edge region 153, 453A through 453G, associated with the exampleresonators 100, 400A through 400G. Similarly, a laterally opposingetched edge region 154, 454A through 454G is arranged laterally opposingor opposite from the notional heavy dashed line depicting the etchededge region 153, 453A through 453G. The etched edge region may, but neednot, assist with acoustic isolation of the resonators. The etched edgeregion may, but need not, help with avoiding acoustic losses for theresonators. The etched edge region 153, 453A through 453G, (and thelaterally opposing etched edge region 154, 454A through 454G) may extendalong the thickness dimension T27 of the piezoelectric layer stack 104,404A through 404G. The etched edge region 153, 453A through 453G, mayextend through (e.g., entirely through or partially through) thepiezoelectric layer stack 104, 404A through 404G. Similarly, thelaterally opposing etched edge region 154, 454A through 454G may extendthrough (e.g., entirely through or partially through) the piezoelectriclayer stack 104, 404A through 404G. The etched edge region 153, 453Athrough 453G, (and the laterally opposing etched edge region 154, 454Athrough 454G) may extend through (e.g., entirely through or partiallythrough) the bottom piezoelectric layer 105, 405A through 405G. Theetched edge region 153, 453A through 453G, (and the laterally opposingetched edge region 154, 454A through 454G) may extend through (e.g.,entirely through or partially through) the first middle piezoelectriclayer 107, 407A through 407G. The etched edge region 153, 453A through453G, (and the laterally opposing etched edge region 154, 454A through454G) may extend through (e.g., entirely through or partially through)the second middle piezoelectric layer 109, 409A through 409G. The etchededge region 153, 453A through 453G, (and the laterally opposing etchededge region 154, 454A through 454G) may extend through (e.g., entirelythrough or partially through) the top piezoelectric layer 111, 411Athrough 411G.

The etched edge region 153, 453A through 453G, (and the laterallyopposing etched edge region 154, 454A through 454G) may extend along thethickness dimension T23 of the bottom acoustic reflector 113, 413Athrough 413G. The etched edge region 153, 453A through 453G, (and thelaterally opposing etched edge region 154, 454A through 454G) may extendthrough (e.g., entirely through or partially through) the bottomacoustic reflector 113, 413A through 413G. The etched edge region 153,453A through 453G, (and the laterally opposing etched edge region 154,454A through 454G) may extend through (e.g., entirely through orpartially through) the initial bottom metal electrode layer 117, 417Athrough 417G. The etched edge region 153, 453A through 453G, (and thelaterally opposing etched edge region 154, 454A through 454G) may extendthrough (e.g., entirely through or partially through) the first pair ofbottom metal electrode layers, 119, 419A through 419G, 121, 421A through421G. The etched edge region 153, 453A through 453G (and the laterallyopposing etched edge region 154, 454A through 454G) may extend through(e.g., entirely through or partially through) the second pair of bottommetal electrode layers, 123, 423A through 423G, 125, 425A through 425G.The etched edge region 153, 453A through 453G (and the laterallyopposing etched edge region 154, 454A through 454G) may extend through(e.g., entirely through or partially through) the third pair of bottommetal electrode layers, 127, 427D, 129, 429D. The etched edge region153, 453A through 453G (and the laterally opposing etched edge region154, 454A through 454G) may extend through (e.g., entirely through orpartially through) the fourth pair of bottom metal electrode layers,131, 431D, 133, 433D.

The etched edge region 153, 453A through 453G (and the laterallyopposing etched edge region 154, 454A through 454G) may extend along thethickness dimension T25 of the top acoustic reflector 115, 415A through415G. The etched edge region 153, 453A through 453G (and the laterallyopposing etched edge region 154, 454A through 454G) may extend through(e.g., entirely through or partially through) the top acoustic reflector115, 415A through 415G. The etched edge region 153, 453A through 453G(and the laterally opposing etched edge region 154, 454A through 454G)may extend through (e.g., entirely through or partially through) theinitial top metal electrode layer 135, 435A through 435G. The etchededge region 153, 453A through 453G (and the laterally opposing etchededge region 154, 454A through 454G) may extend through (e.g., entirelythrough or partially through) the first pair of top metal electrodelayers, 137, 437A through 437G, 139, 439A through 49G. The etched edgeregion 153, 453A through 453C (and the laterally opposing etched edgeregion 154, 454A through 454C) may extend through (e.g., entirelythrough or partially through) the second pair of top metal electrodelayers, 141, 441A through 441C, 143, 443A through 443C. The etched edgeregion 153, 453A through 453C (and the laterally opposing etched edgeregion 154, 454A through 454C) may extend through (e.g., entirelythrough or partially through) the third pair of top metal electrodelayers, 145, 445A through 445C, 147, 447A through 447C. The etched edgeregion 153, 453A through 453C (and the laterally opposing etched edgeregion 154, 454A through 454C) may extend through (e.g., entirelythrough or partially through) the fourth pair of top metal electrodelayers, 149, 449A through 449C, 151, 451A through 451C.

As mentioned previously, mesa structure 104, 404A through 404G (e.g.,first mesa structure 104, 404A through 404G) may comprise the respectivestack 104, 404A through 404G, of the example four layers ofpiezoelectric material. The mesa structure 104, 404A through 404G (e.g.,first mesa structure 104, 404A through 404G) may extend laterallybetween (e.g., may be formed between) etched edge region 153, 453Athrough 453G and laterally opposing etched edge region 154, 454A through454G. As mentioned previously, another mesa structure 113, 413A through413G, (e.g., second mesa structure 113, 413A through 413G), may comprisethe bottom acoustic reflector 113, 413A through 413G. The another mesastructure 113, 413A through 413G, (e.g., second mesa structure 113, 413Athrough 413G) may extend laterally between (e.g., may be formed between)etched edge region 153, 453A through 453G and laterally opposing etchededge region 154, 454A through 454G. As mentioned previously, yet anothermesa structure 115, 415A through 415G, (e.g., third mesa structure 115,415A through 415G), may comprise the top acoustic reflector 115, 415Athrough 415G or a portion of the top acoustic reflector 115, 415Athrough 415G. The yet another mesa structure 115, 415A through 415G,(e.g., third mesa structure 115, 415A through 415G) may extend laterallybetween (e.g., may be formed between) etched edge region 153, 453Athrough 453G and laterally opposing etched edge region 154, 454A through454G. In some example resonators 100, 400A, 400B, 400D through 400F, thesecond mesa structure corresponding to the bottom acoustic reflector113, 413A, 413B, 413D through 413F may be laterally wider than the firstmesa structure corresponding to the stack 104, 404A, 404B, 404D through404F, of the example four layers of piezoelectric material. In someexample resonators 100, 400A through 400C, the first mesa structurecorresponding to the stack 104, 404A through 404C, of the example fourlayers of piezoelectric material may be laterally wider than the thirdmesa structure corresponding to the top acoustic reflector 115, 415Athrough 415C. In some example resonators 400D through 400G, the firstmesa structure corresponding to the stack 404D through 404G, of theexample four layers of piezoelectric material may be laterally widerthan a portion of the third mesa structure corresponding to the topacoustic reflector 415D through 415G.

An optional mass load layer 155, 455A through 455G, may be added to theexample resonators 100, 400A through 400G. For example, filters mayinclude series connected resonator designs and shunt connected resonatordesigns that may include mass load layers. For example, for ladderfilter designs, the shunt resonator may include a sufficient mass loadlayer so that the parallel resonant frequency (Fp) of the shuntresonator approximately matches the series resonant frequency (Fs) ofthe series resonator design. Thus the series resonator design (withoutthe mass load layer) may be used for the shunt resonator design, butwith the addition of the mass load layer 155, 455A through 455G, for theshunt resonator design. By including the mass load layer, the design ofthe shunt resonator may be approximately downshifted, or reduced, infrequency relative to the series resonator by a relative amountapproximately corresponding to the electromechanical couplingcoefficient (Kt2) of the shunt resonator. For the example resonators100, 400A through 400G, the optional mass load layer 155, 455A through455G, may be arranged in the top acoustic reflector 115, 415A through415G, above the first pair of top metal electrode layers. A metal may beused for the mass load. A dense metal such as Tungsten may be used forthe mass load 155, 455A through 455G. An example thickness dimension ofthe optional mass load layer 155, 455A through 455G, may be about onehundred Angstroms (100 A).

However, it should be understood that the thickness dimension of theoptional mass load layer 155, 455A through 455G, may be varied dependingon how much mass loading is desired for a particular design anddepending on which metal is used for the mass load layer. Since theremay be less acoustic energy in the top acoustic reflector 115, 415Athrough 415G, at locations further away from the piezoelectric stack104, 404A through 404G, there may be less acoustic energy interactionwith the optional mass load layer, depending on the location of the massload layer in the arrangement of the top acoustic reflector.Accordingly, in alternative arrangements where the mass load layer isfurther away from the piezoelectric stack 104, 404A through 404G, suchalternative designs may use more mass loading (e.g., thicker mass loadlayer) to achieve the same effect as what is provided in more proximatemass load placement designs. Also, in other alternative arrangements themass load layer may be arranged relatively closer to the piezoelectricstack 104, 404A through 404G. Such alternative designs may use less massloading (e.g., thinner mass load layer). This may achieve the same orsimilar mass loading effect as what is provided in previously discussedmass load placement designs, in which the mass load is arranged lessproximate to the piezoelectric stack 104, 404A through 404G. Similarly,since Titanium (Ti) or Aluminum (Al) is less dense than Tungsten (W) orMolybdenum (Mo), in alternative designs where Titanium or Aluminum isused for the mass load layer, a relatively thicker mass load layer ofTitanium (Ti) or Aluminum (Al) is needed to produce the same mass loadeffect as a mass load layer of Tungsten (W) or Molybdenum (Mo) of agiven mass load layer thickness. Moreover, in alternative arrangementsboth shunt and series resonators may be additionally mass-loaded withconsiderably thinner mass loading layers (e.g., having thickness ofabout one tenth of the thickness of a main mass loading layer) in orderto achieve specific filter design goals, as may be appreciated by oneskilled in the art.

The example resonators 100, 400A through 400G, of FIG. 1A and FIGS. 4Athrough 4G may include a plurality of lateral features 157, 457A through457G (e.g., patterned layer 157, 457A through 457G, e.g., step massfeatures 157, 457A through 457G), sandwiched between two top metalelectrode layers (e.g., between the second member 139, 439A through439G, of the first pair of top metal electrode layers and the firstmember 141, 441A through 441G, of the second pair of top metal electrodelayers) of the top acoustic reflector 115, 415A through 415G. As shownin the figures, the plurality of lateral features 157, 457A through457G, of patterned layer 157, 457A through 457G may comprise stepfeatures 157, 457A through 457G (e.g., step mass features 157, 457Athrough 457G). As shown in the figures, the plurality of lateralfeatures 157, 457A through 457G, may be arranged proximate to lateralextremities (e.g., proximate to a lateral perimeter) of the top acousticreflector 115, 415A through 415G. At least one of the lateral features157, 457A through 457G, may be arranged proximate to where the etchededge region 153, 453A through 453G, extends through the top acousticreflector 115, 415A through 415G.

After the lateral features 157, 457A through 457G, are formed, they mayfunction as a step feature template, so that subsequent top metalelectrode layers formed on top of the lateral features 157, 457A through457G, may retain step patterns imposed by step features of the lateralfeatures 157, 457A through 457G. For example, the second pair of topmetal electrode layers 141, 441A through 441G, 143, 443A through 443G,the third pair of top metal electrode layers 145, 445A through 445C,147, 447A through 447C, and the fourth pair of top metal electrodes 149,449A through 449C, 151, 451A through 451C, may retain step patternsimposed by step features of the lateral features 157, 457A through 457G.The plurality of lateral features 157, 457A through 457G, may add alayer of mass loading. The plurality of lateral features 157, 457Athrough 457G, may be made of a patterned metal layer (e.g., a patternedlayer of Tungsten (W), Molybdenum (Mo), Titanium (Ti), or Aluminum(Al)). In alternative examples, the plurality of lateral features 157,457A through 457G, may be made of a patterned dielectric layer (e.g., apatterned layer of Silicon Nitride (SiN), Silicon Dioxide (SiO2) orSilicon Carbide (SiC)). The plurality of lateral features 157, 457Athrough 457G, may, but need not, limit parasitic lateral acoustic modes(e.g., facilitate suppression of spurious modes) of the exampleresonators 100, 400A through 400G. Thickness of the patterned layer ofthe lateral features 157, 457A through 457G (e.g., thickness of thepatterned layers 157, 457A through 457G), may be adjusted. For example,for the 24 GHz resonator, thickness may be adjusted within a range fromabout fifty Angstroms (50 A) to about five hundred Angstroms (500 A).Lateral step width of the lateral features 157, 457A through 457G (e.g.,width of the step mass features 157, 457A through 457G) may be adjusteddown, for example, from about two microns (2 um). The foregoing may beadjusted to balance a design goal of limiting parasitic lateral acousticmodes (e.g., facilitating suppression of spurious modes) of the exampleresonators 100, 400A through 400G as well as increasing average qualityfactor above the series resonance frequency against other designconsiderations e.g., maintaining desired average quality factor belowthe series resonance frequency.

In the example bulk acoustic wave resonator 100 shown in FIG. 1A, thepatterned layer 157 may comprise Tungsten (W) (e.g., the step massfeature 157 of the patterned layer may comprise Tungsten (W)). Asuitable thickness of the patterned layer 157 (e.g., thickness of thestep mass feature 157) and lateral width of features of the patternedlayer 157 may vary based on various design parameters e.g., materialselected for the patterned layer 157, e.g., the desired resonantfrequency of the given resonant design, e.g., effectiveness infacilitating spurious mode suppression. For an example 24 GHz design ofthe example bulk acoustic wave resonator 100 shown in FIG. 1A in whichthe patterned layer comprises Tungsten (W), a suitable thickness of thepatterned layer 157 (e.g., thickness of the step mass feature 157) maybe 200 Angstroms and lateral width of features of the patterned layer157 (e.g., lateral width of the step mass feature 157) may be 0.8microns, may facilitate suppression of the average strength of thespurious modes in the passband by approximately fifty percent (50%), asestimated by simulation relative to similar designs without the benefitof patterned layer 157.

The example resonators 100, 400A through 400G, of FIG. 1A and FIGS. 4Athrough 4G may include one or more (e.g., one or a plurality of)interposer layers sandwiched between piezoelectric layers of the stack104, 404A through 404G. For example, a first interposer layer 159, 459Athrough 459G may be sandwiched between the bottom piezoelectric layer105, 405A through 405G, and the first middle piezoelectric layer 107,407A through 407G. For example, a second interposer layer 161, 461Athrough 461G, may be sandwiched between the first middle piezoelectriclayer 107, 407A through 407G, and the second middle piezoelectric layer109, 409A through 409G. For example, a third interposer layer 163, 463Athrough 463G, may be sandwiched between the second middle piezoelectriclayer 109, 409A through 409G, and the top piezoelectric layer 111, 411Athrough 411G.

One or more (e.g., one or a plurality of) interposer layers may be metalinterposer layers. The metal interposer layers may be relatively highacoustic impedance metal interposer layers (e.g., using relatively highacoustic impedance metals such as Tungsten (W), or Molybdenum). Suchmetal interposer layers may (but need not) flatten stress distributionacross adjacent piezoelectric layers, and may (but need not) raiseeffective electromechanical coupling coefficient (Kt2) of adjacentpiezoelectric layers.

Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may be dielectric interposer layers. The dielectric ofthe dielectric interposer layers may be a dielectric that has a positiveacoustic velocity temperature coefficient, so acoustic velocityincreases with increasing temperature of the dielectric. The dielectricof the dielectric interposer layers may be, for example, silicondioxide. Dielectric interposer layers may, but need not, facilitatecompensating for frequency response shifts with increasing temperature.Most materials (e.g., metals, e.g., dielectrics) generally have anegative acoustic velocity temperature coefficient, so acoustic velocitydecreases with increasing temperature of such materials. Accordingly,increasing device temperature generally causes response of resonatorsand filters to shift downward in frequency. Including dielectric (e.g.,silicon dioxide) that instead has a positive acoustic velocitytemperature coefficient may facilitate countering or compensating (e.g.,temperature compensating) this downward shift in frequency withincreasing temperature. Alternatively or additionally, one or more(e.g., one or a plurality of) interposer layers may comprise metal anddielectric for respective interposer layers. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may comprise different metals for respective interposer layers.Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may comprise different dielectrics for respectiveinterposer layers.

In addition to the foregoing application of metal interposer layers toraise effective electromechanical coupling coefficient (Kt2) of adjacentpiezoelectric layers, and the application of dielectric interposerlayers to facilitate compensating for frequency response shifts withincreasing temperature, interposer layers may, but need not, increasequality factor (Q-factor) and/or suppress irregular spectral responsepatterns characterized by sharp reductions in Q-factor known as“rattles”. Q-factor of a resonator is a figure of merit in whichincreased Q-factor indicates a lower rate of energy loss per cyclerelative to the stored energy of the resonator. Increased Q-factor inresonators used in filters results in lower insertion loss and sharperroll-off in filters. The irregular spectral response patternscharacterized by sharp reductions in Q-factor known as “rattles” maycause ripples in filter pass bands.

Metal and/or dielectric interposer layer of suitable thicknesses andacoustic material properties (e.g., velocity, density) may be placed atappropriate places in the stack 104, 404A through 404G, of piezoelectriclayers, for example, proximate to the nulls of acoustic energydistribution in the stacks (e.g., between interfaces of piezoelectriclayers of opposing axis orientation). Finite Element Modeling (FEM)simulations and varying parameters in fabrication prior to subsequenttesting may help to optimize interposer layer designs for the stack.Thickness of interposer layers may, but need not, be adjusted toinfluence increased Q-factor and/or rattle suppression. It is theorizedthat if the interposer layer is too thin there is no substantial effect.Thus minimum thickness for the interposer layer may be about onemono-layer, or about five Angstroms (5 A). Alternatively, if theinterposer layer is too thick, rattle strength may increase rather thanbeing suppressed. Accordingly, an upper limit of interposer thicknessmay be about five-hundred Angstroms (500 A) for a twenty-four Gigahertz(24 GHz) resonator design, with limiting thickness scaling inverselywith frequency for alternative resonator designs. It is theorized thatbelow a series resonant frequency of resonators, Fs, Q-factor may not besystematically and significantly affected by including a singleinterposer layer. However, it is theorized that there may, but need not,be significant increases in Q-factor, for example from abouttwo-thousand (2000) to about three-thousand (3000), for inclusion of twoor more interposer layers.

In the example resonators 100, 400A through 400C, of FIG. 1A and FIGS.4A through 4C, a planarization layer 165, 465A through 465C may beincluded. A suitable material may be used for planarization layer 165,465A through 465C, for example Silicon Dioxide (SiO2), Hafnium Dioxide(HfO2), polyimide, or BenzoCyclobutene (BCB). An isolation layer 167,467A through 467C, may also be included and arranged over theplanarization layer 165, 465A-465C. A suitable low dielectric constant(low-k), low acoustic impedance (low-Za) material may be used for theisolation layer 167, 467A through 467C, for example polyimide, orBenzoCyclobutene (BCB).

In the example resonators 100, 400A through 400G, of FIG. 1A and FIGS.4A through 4G, a bottom electrical interconnect 169, 469A through 469G,may be included to interconnect electrically with (e.g., electricallycontact with) the bottom acoustic reflector 113, 413A through 413G,stack of the plurality of bottom metal electrode layers. A topelectrical interconnect 171, 471A through 471G, may be included tointerconnect electrically with the top acoustic reflector 115, 415Athrough 415G, stack of the plurality of top metal electrode layers. Asuitable material may be used for the bottom electrical interconnect169, 469A through 469G, and the top electrical interconnect 171, 471Athrough 471G, for example, gold (Au). Top electrical interconnect 171,471A through 471G may be substantially acoustically isolated from thestack 104, 404A through 404G of the example four layers of piezoelectricmaterial by the top multilayer metal acoustic reflector electrode 115,415A through 415G. Top electrical interconnect 171, 471A through 471Gmay have dimensions selected so that the top electrical interconnect171, 471A through 471G approximates a fifty ohm electrical transmissionline at the main resonant frequency of the bulk acoustic wave resonator100, 400A through 400G. Top electrical interconnect 171, 471A through471G may have a thickness that is substantially thicker than a thicknessof a pair of top metal electrode layers of the top multilayer metalacoustic reflector electrode 115, 415A through 415G (e.g., thicker thanthickness of the first pair of top metal electrode layers 137, 437Athrough 437G, 139, 439A through 439G). Top electrical interconnect 171,471A through 471G may have a thickness within a range from about onehundred Angstroms (100 A) to about five micrometers (5 um). For example,top electrical interconnect 171, 471A through 471G may have a thicknessof about two thousand Angstroms (2000 A).

FIG. 1B is a simplified view of FIG. 1A that illustrates an example ofacoustic stress distribution during electrical operation of the bulkacoustic wave resonator structure shown in FIG. 1A. A notional curvedline schematically depicts vertical (Tzz) stress distribution 173through stack 104 of the example four piezoelectric layers, 105, 107,109, 111. The stress 173 is excited by the oscillating electric fieldapplied via the top acoustic reflector 115 stack of the plurality of topmetal electrode layers 135, 137, 139, 141, 143, 145, 147, 149, 151, andthe bottom acoustic reflector 113 stack of the plurality of bottom metalelectrode layers 117, 119, 121, 123, 125, 127, 129, 131, 133. The stress173 may have maximum values inside the stack 104 of piezoelectriclayers, while exponentially tapering off within the top acousticreflector 115 and the bottom acoustic reflector 113. Notably, acousticenergy confined in the resonator structure 100 is proportional to stressmagnitude.

As discussed previously herein, the example four piezoelectric layers,105, 107, 109, 111 in the stack 104 may have an alternating axisarrangement in the stack 104. For example the bottom piezoelectric layer105 may have the normal axis orientation, which is depicted in FIG. 1Busing the downward directed arrow. Next in the alternating axisarrangement of the stack 104, the first middle piezoelectric layer 107may have the reverse axis orientation, which is depicted in FIG. 1Busing the upward directed arrow. Next in the alternating axisarrangement of the stack 104, the second middle piezoelectric layer 109may have the normal axis orientation, which is depicted in FIG. 1B usingthe downward directed arrow. Next in the alternating axis arrangement ofthe stack 104, the top piezoelectric layer 111 may have the reverse axisorientation, which is depicted in FIG. 1B using the upward directedarrow. For the alternating axis arrangement of the stack 104, stress 173excited by the applied oscillating electric field causes normal axispiezoelectric layers (e.g., bottom and second middle piezoelectriclayers 105, 109) to be in compression, while reverse axis piezoelectriclayers (e.g., first middle and top piezoelectric layers 107, 111) to bein extension. Accordingly, FIG. 1B shows peaks of stress 173 on theright side of the heavy dashed line to depict compression in normal axispiezoelectric layers (e.g., bottom and second middle piezoelectriclayers 105, 109), while peaks of stress 173 are shown on the left sideof the heavy dashed line to depict extension in reverse axispiezoelectric layers (e.g., first middle and top piezoelectric layers107, 111).

FIG. 1C shows a simplified top plan view of a bulk acoustic waveresonator structure 100A corresponding to the cross sectional view ofFIG. 1A, and also shows another simplified top plan view of analternative bulk acoustic wave resonator structure 100B. The bulkacoustic wave resonator structure 100A may include the stack 104A offour layers of piezoelectric material e.g., having the alternatingpiezoelectric axis arrangement of the four layers of piezoelectricmaterial. The stack 104A of piezoelectric layers may be sandwichedbetween the bottom acoustic reflector electrode 113A and the topacoustic reflector electrode 115A. The bottom acoustic reflectorelectrode may comprise the stack of the plurality of bottom metalelectrode layers of the bottom acoustic reflector electrode 113A, e.g.,having the alternating arrangement of low acoustic impedance bottommetal electrode layers and high acoustic impedance bottom metal layers.Similarly, the top acoustic reflector electrode 115A may comprise thestack of the plurality of top metal electrode layers of the top acousticreflector electrode 115A, e.g., having the alternating arrangement oflow acoustic impedance top metal electrode layers and high acousticimpedance top metal electrode layers. The top acoustic reflectorelectrode 115A may include a patterned layer 157A. The patterned layer157A may approximate a frame shape (e.g., rectangular frame shape)proximate to a perimeter (e.g., rectangular perimeter) of top acousticreflector electrode 115A as shown in simplified top plan view in FIG.1C. This patterned layer 157A, e.g., approximating the rectangular frameshape in the simplified top plan view in FIG. 1C, corresponds to thepatterned layer 157 shown in simplified cross sectional view in FIG. 1A.Top electrical interconnect 171A extends over (e.g., electricallycontacts) top acoustic reflector electrode 115A. Bottom electricalinterconnect 169A extends over (e.g., electrically contacts) bottomacoustic reflector electrode 113A through bottom via region 168A.

FIG. 1C also shows another simplified top plan view of an alternativebulk acoustic wave resonator structure 100B. Similarly, the bulkacoustic wave resonator structure 100B may include the stack 104B offour layers of piezoelectric material e.g., having the alternatingpiezoelectric axis arrangement of the four layers of piezoelectricmaterial. The stack 104B of piezoelectric layers may be sandwichedbetween the bottom acoustic reflector electrode 113B and the topacoustic reflector electrode 115B. The bottom acoustic reflectorelectrode may comprise the stack of the plurality of bottom metalelectrode layers of the bottom acoustic reflector electrode 113B, e.g.,having the alternating arrangement of low acoustic impedance bottommetal electrode layers and high acoustic impedance bottom metal layers.Similarly, the top acoustic reflector electrode 115B may comprise thestack of the plurality of top metal electrode layers of the top acousticreflector electrode 115B, e.g., having the alternating arrangement oflow acoustic impedance top metal electrode layers and high acousticimpedance top metal electrode layers. The top acoustic reflectorelectrode 115B may include a patterned layer 157B. The patterned layer157B may approximate a frame shape (e.g., apodized frame shape)proximate to a perimeter (e.g., apodized perimeter) of top acousticreflector electrode 115B as shown in simplified top plan view in FIG.1C. The apodized frame shape may be a frame shape in which substantiallyopposing extremities are not parallel to one another. This patternedlayer 157B, e.g., approximating the apodized frame shape in thesimplified top plan view in FIG. 1C, is an alternative embodimentcorresponding to the patterned layer 157 shown in simplified crosssectional view in FIG. 1A. Top electrical interconnect 171B extends over(e.g., electrically contacts) top acoustic reflector electrode 115B.Bottom electrical interconnect 169B extends over (e.g., electricallycontacts) bottom acoustic reflector electrode 113B through bottom viaregion 168B.

In FIGS. 1D and 1E, Nitrogen (N) atoms are depicted with a hatchingstyle, while Aluminum (Al) atoms are depicted without a hatching style.FIG. 1D is a perspective view of an illustrative model of a reverse axiscrystal structure 175 of Aluminum Nitride, AlN, in piezoelectricmaterial of layers in FIG. 1A, e.g., having reverse axis orientation ofnegative polarization. For example, first middle and top piezoelectriclayers 107, 111 discussed previously herein with respect to FIGS. 1A and1B are reverse axis piezoelectric layers. By convention, when the firstlayer of normal axis crystal structure 175 is a Nitrogen, N, layer andsecond layer in an upward direction (in the depicted orientation) is anAluminum, Al, layer, the piezoelectric material including the reverseaxis crystal structure 175 is said to have crystallographic c-axisnegative polarization, or reverse axis orientation as indicated by theupward pointing arrow 177. For example, polycrystalline thin filmAluminum Nitride, AlN, may be grown in the crystallographic c-axisnegative polarization, or reverse axis, orientation perpendicularrelative to the substrate surface using reactive magnetron sputtering ofan aluminum target in a nitrogen atmosphere, and by introducing oxygeninto the gas atmosphere of the reaction chamber during fabrication atthe position where the flip to the reverse axis is desired. An inertgas, for example, Argon may also be included in a sputtering gasatmosphere, along with the nitrogen and oxygen.

For example, a predetermined amount of oxygen containing gas may beadded to the gas atmosphere over a short predetermined period of time orfor the entire time the reverse axis layer is being deposited. Theoxygen containing gas may be diatomic oxygen containing gas, such asoxygen (O2). Proportionate amounts of the Nitrogen gas (N2) and theinert gas may flow, while the predetermined amount of oxygen containinggas flows into the gas atmosphere over the predetermined period of time.For example, N2 and Ar gas may flow into the reaction chamber inapproximately a 3:1 ratio of N2 to Ar, as oxygen gas also flows into thereaction chamber. For example, the predetermined amount of oxygencontaining gas added to the gas atmosphere may be in a range from abouta thousandth of a percent (0.001%) to about ten percent (10%), of theentire gas flow. The entire gas flow may be a sum of the gas flows ofargon, nitrogen and oxygen, and the predetermined period of time duringwhich the predetermined amount of oxygen containing gas is added to thegas atmosphere may be in a range from about a quarter (0.25) second to alength of time needed to create an entire layer, for example. Forexample, based on mass-flows, the oxygen composition of the gasatmosphere may be about 2 percent when the oxygen is briefly injected.This results in an aluminum oxynitride (ALON) portion of the finalmonolithic piezoelectric layer, integrated in the Aluminum Nitride, AlN,material, having a thickness in a range of about 5 nm to about 20 nm,which is relatively oxygen rich and very thin. Alternatively, the entirereverse axis piezoelectric layer may be aluminum oxynitride.

FIG. 1E is a perspective view of an illustrative model of a normal axiscrystal structure 179 of Aluminum Nitride, AlN, in piezoelectricmaterial of layers in FIG. 1A, e.g., having normal axis orientation ofpositive polarization. For example, bottom and second middlepiezoelectric layers 105, 109 discussed previously herein with respectto FIGS. 1A and 1B are normal axis piezoelectric layers. By convention,when the first layer of the reverse axis crystal structure 179 is an Allayer and second layer in an upward direction (in the depictedorientation) is an N layer, the piezoelectric material including thereverse axis crystal structure 179 is said to have a c-axis positivepolarization, or normal axis orientation as indicated by the downwardpointing arrow 181. For example, polycrystalline thin film AlN may begrown in the crystallographic c-axis positive polarization, or normalaxis, orientation perpendicular relative to the substrate surface byusing reactive magnetron sputtering of an Aluminum target in a nitrogenatmosphere.

FIGS. 2A and 2B show a further simplified view of a bulk acoustic waveresonator similar to the bulk acoustic wave resonator structure shown inFIG. 1A along with its corresponding impedance versus frequency responseduring its electrical operation, as well as alternative bulk acousticwave resonator structures with differing numbers of alternating axispiezoelectric layers, and their respective corresponding impedanceversus frequency response during electrical operation. FIG. 2C showsadditional alternative bulk acoustic wave resonator structures withadditional numbers of alternating axis piezoelectric layers. Bulkacoustic wave resonators 2001A through 2001I may, but need not be, bulkacoustic millimeter wave resonators 2001A through 2001I, operable with amain resonance mode having a main resonant frequency that is amillimeter wave frequency (e.g., twenty-four Gigahertz, 24 GHz) in amillimeter wave frequency band. As defined herein, millimeter wave meansa wave having a frequency within a range extending from eight Gigahertz(8 GHz) to three hundred Gigahertz (300 GHz), and millimeter wave bandmeans a frequency band spanning this millimeter wave frequency rangefrom eight Gigahertz (8 GHz) to three hundred Gigahertz (300 GHz). Bulkacoustic wave resonators 2001A through 2001I may, but need not be, bulkacoustic Super High Frequency (SHF) wave resonators 2001A through 2001Ior bulk acoustic Extremely High Frequency (EHF) wave resonators 2001Athrough 2001I, as the terms Super High Frequency (SHF) and ExtremelyHigh Frequency (EHF) are defined by the International TelecommunicationsUnion (ITU). For example, bulk acoustic wave resonators 2001A through2001I may be bulk acoustic Super High Frequency (SHF) wave resonators2001A through 2001I operable with a main resonance mode having a mainresonant frequency that is a Super High Frequency (SHF) (e.g.,twenty-four Gigahertz, 24 GHz) in a Super High Frequency (SHF) wavefrequency band. Piezoelectric layer thicknesses may be selected todetermine the main resonant frequency of bulk acoustic Super HighFrequency (SHF) wave resonators 2001A through 2001I in the Super HighFrequency (SHF) wave band (e.g., twenty-four Gigahertz, 24 GHz mainresonant frequency). Similarly, layer thicknesses of Super HighFrequency (SHF) reflector layers (e.g., layer thickness of multilayermetal acoustic SHF wave reflector bottom electrodes 2013A through 2013I,e.g., layer thickness of multilayer metal acoustic SHF wave reflectortop electrodes 2015A through 2015I) may be selected to determine peakacoustic reflectivity of such SHF reflectors at a frequency, e.g., peakreflectivity resonant frequency, within the Super High Frequency (SHF)wave band (e.g., a twenty-four Gigahertz, 24 GHz peak reflectivityresonant frequency). Alternatively, bulk acoustic wave resonators 2001Athrough 2001I may be bulk acoustic Extremely High Frequency (EHF) waveresonators 2001A through 2001I operable with a main resonance modehaving a main resonant frequency that is an Extremely High Frequency(EHF) wave band (e.g., thirty-nine Gigahertz, 39 GHz main resonantfrequency) in an Extremely High Frequency (EHF) wave frequency band.Piezoelectric layer thicknesses may be selected to determine the mainresonant frequency of bulk acoustic Extremely High Frequency (EHF) waveresonators 2001A through 2001I in the Extremely High Frequency (EHF)wave band (e.g., thirty-nine Gigahertz, 39 GHz main resonant frequency).Similarly, layer thicknesses of Extremely High Frequency (EHF) reflectorlayers (e.g., layer thickness of multilayer metal acoustic EHF wavereflector bottom electrodes 2013A through 2013I, e.g., layer thicknessof multilayer metal acoustic EHF wave reflector top electrodes 2015Athrough 2015I) may be selected to determine peak acoustic reflectivityof such EHF reflectors at a frequency, e.g., peak reflectivity resonantfrequency, within the Extremely High Frequency (EHF) wave band (e.g., athirty-nine Gigahertz, 39 GHz peak reflectivity resonant frequency). Thegeneral structures of the multilayer metal acoustic reflector topelectrode and the multilayer metal acoustic reflector bottom electrodehave already been discussed previously herein with respect of FIGS. 1Aand 1B. As already discussed, these structures are directed torespective pairs of metal electrode layers, in which a first member ofthe pair has a relatively low acoustic impedance (relative to acousticimpedance of an other member of the pair), in which the other member ofthe pair has a relatively high acoustic impedance (relative to acousticimpedance of the first member of the pair), and in which the respectivepairs of metal electrode layers have layer thicknesses corresponding toone quarter wavelength (e.g., one quarter acoustic wavelength) at a mainresonant frequency of the resonator. Accordingly, it should beunderstood that the bulk acoustic millimeter wave resonators 2001A,2001B, 2000C shown in FIG. 2A include respective multilayer metalacoustic millimeter wave reflector top electrodes 2015A, 2015B, 2015Cand multilayer metal acoustic millimeter wave reflector bottomelectrodes 2013A, 2013B, 2013C, in which the respective pairs of metalelectrode layers have layer thicknesses corresponding to a quarterwavelength (e.g., one quarter of an acoustic wavelength) at a millimeterwave main resonant frequency of the respective bulk acoustic millimeterwave resonator 2001A, 2001B, 2001C.

Shown in FIG. 2A is a bulk acoustic millimeter wave resonator 2001Aincluding a normal axis piezoelectric layer 201A sandwiched betweenmultilayer metal acoustic millimeter wave reflector top electrode 2015Aand multilayer metal acoustic millimeter wave reflector bottom electrode2013A. Also shown in FIG. 2A is a bulk acoustic millimeter waveresonator 2001B including a normal axis piezoelectric layer 201B and areverse axis piezoelectric layer 202B arranged in a two piezoelectriclayer alternating stack arrangement sandwiched between multilayer metalacoustic millimeter wave reflector top electrode 2015B and multilayermetal acoustic millimeter wave reflector bottom electrode 2013B. A bulkacoustic millimeter wave resonator 2001C includes a normal axispiezoelectric layer 201C, a reverse axis piezoelectric layer 202C, andanother normal axis piezoelectric layer 203C arranged in a threepiezoelectric layer alternating stack arrangement sandwiched betweenmultilayer metal acoustic millimeter wave reflector top electrode 2015Cand multilayer metal acoustic millimeter wave reflector bottom electrode2013C.

Included in FIG. 2B is bulk acoustic millimeter wave resonator 2001D ina further simplified view similar to the bulk acoustic wave resonatorstructure shown in FIGS. 1A and 1B and including a normal axispiezoelectric layer 201D, a reverse axis piezoelectric layer 202D, andanother normal axis piezoelectric layer 203D, and another reverse axispiezoelectric layer 204D arranged in a four piezoelectric layeralternating stack arrangement sandwiched between multilayer metalacoustic millimeter wave reflector top electrode 2015D and multilayermetal acoustic millimeter wave reflector bottom electrode 2013D. A bulkacoustic millimeter wave resonator 2001E includes a normal axispiezoelectric layer 201E, a reverse axis piezoelectric layer 202E,another normal axis piezoelectric layer 203E, another reverse axispiezoelectric layer 204E, and yet another normal axis piezoelectriclayer 205E arranged in a five piezoelectric layer alternating stackarrangement sandwiched between multilayer metal acoustic millimeter wavereflector top electrode 2015E and multilayer metal acoustic millimeterwave reflector bottom electrode 2013E. A bulk acoustic millimeter waveresonator 2001F includes a normal axis piezoelectric layer 201F, areverse axis piezoelectric layer 202F, another normal axis piezoelectriclayer 203F, another reverse axis piezoelectric layer 204F, yet anothernormal axis piezoelectric layer 205F, and yet another reverse axispiezoelectric layer 206F arranged in a six piezoelectric layeralternating stack arrangement sandwiched between multilayer metalacoustic millimeter wave reflector top electrode 2015F and multilayermetal acoustic millimeter wave reflector bottom electrode 2013F.

In FIG. 2A, shown directly to the right of the bulk acoustic millimeterwave resonator 2001A including the normal axis piezoelectric layer 201A,is a corresponding diagram 2019A depicting its impedance versusfrequency response during its electrical operation, as predicted bysimulation. The diagram 2019A depicts the main resonant peak 2021A ofthe main resonant mode of the bulk acoustic millimeter wave resonator2001A at its main resonant frequency (e.g., its 24 GHz series resonantfrequency). The diagram 2019A also depicts the satellite resonance peaks2023A, 2025A of the satellite resonant modes of the bulk acousticmillimeter wave resonator 2001A at satellite frequencies above and belowthe main resonant frequency 2021A (e.g., above and below the 24 GHzseries resonant frequency). Relatively speaking, the main resonant modecorresponding to the main resonance peak 2021A is the strongest resonantmode because it is stronger than all other resonant modes of theresonator 2001A, (e.g., stronger than the satellite modes correspondingto relatively lesser satellite resonance peaks 2023A, 2025A).

Similarly, in FIGS. 2A and 2B, shown directly to the right of the bulkacoustic millimeter wave resonators 2001B through 2001F are respectivecorresponding diagrams 2019B through 2019F depicting correspondingimpedance versus frequency response during electrical operation, aspredicted by simulation. The diagrams 2019B through 2019F depictrespective main resonant peaks 2021B through 2021F of respectivecorresponding main resonant modes of bulk acoustic millimeter waveresonators 2001B through 2001F at respective corresponding main resonantfrequencies (e.g., respective 24 GHz series resonant frequencies). Thediagrams 2019B through 2019F also depict respective satellite resonancepeaks 2023B through 2023F, 2025B through 2025F of respectivecorresponding satellite resonant modes of the bulk acoustic millimeterwave resonators 2001B through 2001F at respective correspondingsatellite frequencies above and below the respective corresponding mainresonant frequencies 2021B through 2021F (e.g., above and below thecorresponding respective 24 GHz series resonant frequencies). Relativelyspeaking, for the corresponding respective main resonant modes, itscorresponding respective main resonance peak 2021B through 2021F is thestrongest for its bulk acoustic millimeter wave resonators 2001B through2001F (e.g., stronger than the corresponding respective satellite modesand corresponding respective lesser satellite resonance peaks 2023B,2025B).

For the bulk acoustic millimeter wave resonator 2001F having thealternating axis stack of six piezoelectric layers, simulation of the 24GHz design predicts an average passband quality factor of approximately1,700. Scaling this 24 Ghz, six piezoelectric layer design to a 37 Ghz,six piezoelectric layer design, may have an average passband qualityfactor of approximately 1,300 as predicted by simulation. Scaling this24 Ghz, six piezoelectric layer design to a 77 Ghz, six piezoelectriclayer design, may have an average passband quality factor ofapproximately 730 as predicted by simulation.

As mentioned previously, FIG. 2C shows additional alternative bulkacoustic wave resonator structures with additional numbers ofalternating axis piezoelectric layers. A bulk acoustic millimeter waveresonator 2001G includes four normal axis piezoelectric layers 201G,203G, 205G, 207G, and four reverse axis piezoelectric layers 202G, 204G,206G, 208G arranged in an eight piezoelectric layer alternating stackarrangement sandwiched between multilayer metal acoustic millimeter wavereflector top electrode 2015G and multilayer metal acoustic millimeterwave reflector bottom electrode 2013G. A bulk acoustic millimeter waveresonator 2001H includes five normal axis piezoelectric layers 201H,203H, 205H, 207H, 209H and five reverse axis piezoelectric layers 202H,204H, 206H, 208H, 210H arranged in a ten piezoelectric layer alternatingstack arrangement sandwiched between multilayer metal acousticmillimeter wave reflector top electrode 2015H and multilayer metalacoustic millimeter wave reflector bottom electrode 2013H. A bulkacoustic millimeter wave resonator 2001I includes nine normal axispiezoelectric layers 201I, 203I, 205I, 207I, 209I, 211I, 213I, 215I,217I and nine reverse axis piezoelectric layers 202I, 204I, 206I, 208I,210I, 212I, 214I, 216I, 218I arranged in an eighteen piezoelectric layeralternating stack arrangement sandwiched between multilayer metalacoustic millimeter wave reflector top electrode 2015I and multilayermetal acoustic millimeter wave reflector bottom electrode 2013I.

For the bulk acoustic millimeter wave resonator 2001I having thealternating axis stack of eighteen piezoelectric layers, simulation ofthe 24 GHz design predicts an average passband quality factor ofapproximately 2,700. Scaling this 24 Ghz, eighteen piezoelectric layerdesign to a 37 Ghz, eighteen piezoelectric layer design, may have anaverage passband quality factor of approximately 2000 as predicted bysimulation. Scaling this 24 Ghz, eighteen piezoelectric layer design toa 77 Ghz, eighteen piezoelectric layer design, may have an averagepassband quality factor of approximately 1,130 as predicted bysimulation.

In the example resonators, 2001A through 2001I, of FIGS. 2A through 2C,a notional heavy dashed line is used in depicting respective etched edgeregion, 253A through 253I, associated with the example resonators, 2001Athrough 2001I. Similarly, in the example resonators, 2001A through2001I, of FIGS. 2A through 2C, a laterally opposed etched edge region254A through 254I may be arranged laterally opposite from etched edgeregion, 253A through 253I. The respective etched edge region may, butneed not, assist with acoustic isolation of the resonators, 2001Athrough 2001I. The respective etched edge region may, but need not, helpwith avoiding acoustic losses for the resonators, 2001A through 2001I.The respective etched edge region, 253A through 253I, (and the laterallyopposed etched edge region 254A through 254I) may extend along thethickness dimension of the respective piezoelectric layer stack. Therespective etched edge region, 253A through 253I, (and the laterallyopposed etched edge region 254A through 254I) may extend through (e.g.,entirely through or partially through) the respective piezoelectriclayer stack. The respective etched edge region, 253A through 253I mayextend through (e.g., entirely through or partially through) therespective first piezoelectric layer, 201A through 201I. The respectiveetched edge region, 253B through 253I, (and the laterally opposed etchededge region 254B through 254I) may extend through (e.g., entirelythrough or partially through) the respective second piezoelectric layer,202B through 202I. The respective etched edge region, 253C through 253I,(and the laterally opposed etched edge region 254C through 254I) mayextend through (e.g., entirely through or partially through) therespective third piezoelectric layer, 203C through 203I. The respectiveetched edge region, 253D through 253I, (and the laterally opposed etchededge region 254D through 254I) may extend through (e.g., entirelythrough or partially through) the respective fourth piezoelectric layer,204D through 204I. The respective etched edge region, 253E through 253I,(and the laterally opposed etched edge region 254E through 254I) mayextend through (e.g., entirely through or partially through) therespective additional piezoelectric layers of the resonators, 2001Ethrough 2001I. The respective etched edge region, 253A through 253I,(and the laterally opposed etched edge region 254A through 254I) mayextend along the thickness dimension of the respective multilayer metalacoustic millimeter wave reflector bottom electrode, 2013A through2013I, of the resonators, 2001A through 2001I. The respective etchededge region, 253A through 253I, (and the laterally opposed etched edgeregion 254A through 254I) may extend through (e.g., entirely through orpartially through) the respective multilayer metal acoustic millimeterwave reflector bottom electrode, 2013A through 2013I. The respectiveetched edge region, 253A through 253I, (and the laterally opposed etchededge region 254A through 254I) may extend along the thickness dimensionof the respective multilayer metal acoustic millimeter wave reflectortop electrode, 2015A through 2015I of the resonators, 2001A through2001I. The etched edge region, 253A through 253I, (and the laterallyopposed etched edge region 254A through 254I) may extend through (e.g.,entirely through or partially through) the respective multilayer metalacoustic millimeter wave reflector top electrode, 2015A through 2015I.

As shown in FIGS. 2A through 2C, first mesa structures corresponding tothe respective stacks of piezoelectric material layers may extendlaterally between (e.g., may be formed between) etched edge regions 253Athrough 253I and laterally opposing etched edge region 254A through254I. Second mesa structures corresponding to multilayer metal acousticmillimeter wave reflector bottom electrode 2013A through 2013I mayextend laterally between (e.g., may be formed between) etched edgeregions 153A through 153I and laterally opposing etched edge region 154Athrough 154I. Third mesa structures corresponding to multilayer metalacoustic millimeter wave reflector top electrode 2015A through 2015I mayextend laterally between (e.g., may be formed between) etched edgeregions 153A through 153I and laterally opposing etched edge region 154Athrough 154I.

In accordance with the teachings herein, various bulk acousticmillimeter wave resonators may include: a seven piezoelectric layeralternating axis stack arrangement; a nine piezoelectric layeralternating axis stack arrangement; an eleven piezoelectric layeralternating axis stack arrangement; a twelve piezoelectric layeralternating axis stack arrangement; a thirteen piezoelectric layeralternating axis stack arrangement; a fourteen piezoelectric layeralternating axis stack arrangement; a fifteen piezoelectric layeralternating axis stack arrangement; a sixteen piezoelectric layeralternating axis stack arrangement; and a seventeen piezoelectric layeralternating axis stack arrangement; and that these stack arrangementsmay be sandwiched between respective multilayer metal acousticmillimeter wave reflector top electrodes and respective multilayer metalacoustic millimeter wave reflector bottom electrodes. Mass load layersand lateral features (e.g., step features) as discussed previouslyherein with respect to FIG. 1A are not explicitly shown in thesimplified diagrams of the various resonators shown in FIGS. 2A, 2B and2C. However, such mass load layers may be included, and such lateralfeatures may be included, and may be arranged between, for example, topmetal electrode layers of the respective top acoustic reflectors of theresonators shown in FIGS. 2A, 2B and 2C. Further, such mass load layersmay be included, and such lateral features may be included, and may bearranged between, for example, top metal electrode layers of therespective top acoustic reflectors in the various resonators having thealternating axis stack arrangements of various numbers of piezoelectriclayers, as described in this disclosure.

In a millimeter wave frequency example (e.g., in a Super High Frequency(SHF) example), thicknesses of piezoelectric layers (e.g., thicknessesof the normal axis piezoelectric layer 2005A through 2005I, e.g.,thicknesses of the reverse axis piezoelectric layer 2007A through 2007I)may determine (e.g., may be selected to determine) the main resonantfrequency of bulk acoustic millimeter wave resonator 2001A through 2001Iin the millimeter wave band (e.g., approximately twenty-four Gigahertz,approximately 24 GHz main resonant frequency). Similarly, in the 24 GHzmillimeter wave example, layer thicknesses of millimeter wave acousticreflector electrode layers (e.g., member layer thicknesses of bottomacoustic millimeter wave reflector electrode 2013A through 2013I, e.g.,member layer thickness of top acoustic millimeter wave reflectorelectrode 2015A through 2015I) may be selected to determine peakacoustic reflectivity of such acoustic millimeter wave reflectorelectrodes at a frequency, e.g., peak reflectivity resonant frequency,within the millimeter wave band (e.g., approximately twenty-fourGigahertz, approximately 24 GHz peak reflectivity resonant frequency).The millimeter wave band may include: 1) peak reflectivity resonantfrequency (e.g., approximately twenty-four Gigahertz, approximately 24GHz peak reflectivity resonant frequency) of the acoustic millimeterwave reflector electrode layers; and 2) the main resonant frequency ofbulk acoustic millimeter wave resonator 2001A through 2001I (e.g.,approximately twenty-four Gigahertz, approximately 24 GHz main resonantfrequency).

In additional millimeter wave frequency examples (e.g., additionalExtremely High Frequency (EHF) examples), thicknesses of piezoelectriclayers (e.g., thicknesses of the normal axis piezoelectric layer 2005Athrough 2005I, e.g., thicknesses of the reverse axis piezoelectric layer2007A through 2007I) may be selected to determine the main resonantfrequency of bulk acoustic millimeter wave resonator 2001A through 2001Iin the millimeter wave frequency band (e.g., 39 GHz main resonantfrequency, e.g., 77 GHz main resonant frequency). Similarly, inadditional millimeter wave frequency examples, layer thicknesses ofacoustic millimeter wave reflector electrode layers (e.g., member layerthicknesses of bottom acoustic millimeter wave reflector electrode 2013Athrough 2013I, e.g., member layer thickness of top acoustic millimeterwave reflector electrode 2015A through 2015I) may be selected todetermine peak acoustic reflectivity of such acoustic millimeter wavereflector electrodes at a frequency, e.g., peak reflectivity resonantfrequency, within the millimeter wave band (e.g., 39 GHz peakreflectivity resonant frequency, e.g., 77 GHz peak reflectivity resonantfrequency). The millimeter wave band may include: 1) peak reflectivityresonant frequency (e.g., 39 GHz peak reflectivity resonant frequency,e.g., 77 GHz peak reflectivity resonant frequency) of the acousticmillimeter wave reflector electrode layers; and 2) the main resonantfrequency of bulk acoustic millimeter wave resonator 2001A through 2001I(e.g., 39 GHz main resonant frequency, e.g., 77 GHz main resonantfrequency).

For example, relatively low acoustic impedance titanium (Ti) metal andrelatively high acoustic impedance Molybdenum (Mo) metal may bealternated for member layers of the bottom acoustic reflector electrode2013A through 2013I, and for member layers of top acoustic reflectorelectrode 2015A through 2015I. Accordingly, these member layers may bedifferent metals from one another having respective acoustic impedancesthat are different from one another so as to provide a reflectiveacoustic impedance mismatch at the resonant frequency of the resonator.For example, a first member may have an acoustic impedance, and a secondmember may have a relatively higher acoustic impedance that is at leastabout twice (e.g., twice) as high as the acoustic impedance of the firstmember.

Thicknesses of member layers of the acoustic reflector electrodes may berelated to resonator resonant frequency. Member layers of the acousticreflector electrodes may be made thinner as resonators are made toextend to higher resonant frequencies, and as acoustic reflectorelectrodes are made to extend to higher peak reflectivity resonantfrequencies. In accordance with teachings of this disclosure, tocompensate for this member layer thinning, number of member layers ofthe acoustic reflector electrodes may be increased in designs extendingto higher resonant frequencies, to facilitate thermal conductivitythrough acoustic reflector electrodes, and to facilitate electricalconductivity through acoustic reflectivity at higher resonantfrequencies. Operation of the example bulk acoustic wave resonators2001A through 2001I at a resonant millimeter wave frequency (e.g., at aresonant Super High Frequency (SHF), e.g., at a resonant Extremely HighFrequency (EHF)) may generate heat to be removed from bulk acoustic waveresonators 2001A through 2001I through the acoustic reflectorelectrodes. The acoustic reflector electrodes (e.g., bottom acousticmillimeter wave reflector electrode 2013A through 2013I, e.g., topacoustic millimeter wave reflector electrode 2015A through 2015I) mayhave thermal resistance of three thousand degrees Kelvin per Watt orless at the given frequency (e.g., at the resonant frequency of the BAWresonator in the millimeter wave frequency band, e.g., at the peakreflectivity resonant frequency of the acoustic reflector electrode inthe millimeter wave frequency band). For example, a sufficient number ofmember layers may be employed to provide for this thermal resistance atthe given frequency (e.g., at the resonant frequency of the BAWresonator in the millimeter wave frequency band, e.g., at the peakreflectivity resonant frequency of the acoustic reflector electrode inthe millimeter wave frequency band).

Further, quality factor (Q factor) is a figure of merit for bulkacoustic wave resonators that may be related, in part, to acousticreflector electrode conductivity. In accordance with the teachings ofthis disclosure, without an offsetting compensation that increasesnumber of member layers, member layer thinning with increasing frequencymay otherwise diminish acoustic reflector electrode conductivity, andmay otherwise diminish quality factor (Q factor) of bulk acoustic waveresonators. In accordance with the teachings of this disclosure, numberof member layers of the acoustic reflector electrodes may be increasedin designs extending to higher resonant frequencies, to facilitateelectrical conductivity through acoustic reflector electrodes. Theacoustic reflector electrodes (e.g., bottom acoustic millimeter wavereflector electrode 2013A through 2013I, e.g., top acoustic millimeterwave reflector electrode 2015A through 2015I) may have sheet resistanceof less than one Ohm per square at the given frequency (e.g., at theresonant frequency of the BAW resonator in the millimeter wave frequencyband, e.g., at the peak reflectivity resonant frequency of the acousticreflector electrode in the millimeter wave frequency band). For example,a sufficient number of member layers may be employed to provide for thissheet resistance at the given frequency (e.g., at the resonant frequencyof the BAW resonator in the millimeter wave frequency band, e.g., at thepeak reflectivity resonant frequency of the acoustic reflector electrodein the millimeter wave band). This may, but need not, facilitateenhancing quality factor (Q factor) to a quality factor (Q factor) thatmay be above a desired one thousand (1000).

Further, it should be understood that interposer layers as discussedpreviously herein with respect to FIG. 1A are explicitly shown in thesimplified diagrams of the various resonators shown in FIGS. 2A, 2B and2C. Such interposers may be included and interposed between adjacentpiezoelectric layers in the various resonators shown in FIGS. 2A, 2B and2C, and further may be included and interposed between adjacentpiezoelectric layers in the various resonators having the alternatingaxis stack arrangements of various numbers of piezoelectric layers, asdescribed in this disclosure. In some other alternative bulk acousticwave resonator structures, fewer interposer layers may be employed. Forexample, FIG. 2D shows another alternative bulk acoustic wave resonatorstructure 2001J, similar to bulk acoustic wave resonator structure 2001Ishown in FIG. 2C, but with differences. For example, relatively fewerinterposer layers may be included in the alternative bulk acoustic waveresonator structure 2001J shown in FIG. 2D. For example, FIG. 2D shows afirst interposer layer 261J interposed between second layer of (reverseaxis) piezoelectric material 202J and third layer of (normal axis)piezoelectric material 203J, but without an interposer layer interposedbetween first layer of (normal axis) piezoelectric material 201J andsecond layer of (reverse axis) piezoelectric material 202J. As shown inFIG. 2D in a first detailed view 220J, without an interposer layerinterposed between first layer of piezoelectric material 201J and secondlayer of piezoelectric material 202J, the first and second piezoelectriclayer 201J, 202J may be a monolithic layer 222J of piezoelectricmaterial (e.g., Aluminum Nitride (AlN)) having first and second regions224J, 226J. A central region of monolithic layer 222J of piezoelectricmaterial (e.g., Aluminum Nitride (AlN)) between first and second regions224J, 226J may be oxygen rich. The first region 224J of monolithic layer222J (e.g., bottom region 224J of monolithic layer 222J) has a firstpiezoelectric axis orientation (e.g., normal axis orientation) asrepresentatively illustrated in detailed view 220J using a downwardpointing arrow at first region 224J, (e.g., bottom region 224J). Thisfirst piezoelectric axis orientation (e.g., normal axis orientation,e.g., downward pointing arrow) at first region 224J of monolithic layer222J (e.g., bottom region 224J of monolithic layer 222J) corresponds tothe first piezoelectric axis orientation (e.g., normal axis orientation,e.g., downward pointing arrow) of first piezoelectric layer 201J. Thesecond region 226J of monolithic layer 222J (e.g., top region 226J ofmonolithic layer 222J) has a second piezoelectric axis orientation(e.g., reverse axis orientation) as representatively illustrated indetailed view 220J using an upward pointing arrow at second region 226J,(e.g., top region 226J). This second piezoelectric axis orientation(e.g., reverse axis orientation, e.g., upward pointing arrow) at secondregion 226J of monolithic layer 222J (e.g., top region 226J ofmonolithic layer 222J) may be formed to oppose the first piezoelectricaxis orientation (e.g., normal axis orientation, e.g., downward pointingarrow) at first region 224J of monolithic layer 222J (e.g., bottomregion 224J of monolithic layer 222J) by adding gas (e.g., oxygen) toflip the axis while sputtering the second region 226J of monolithiclayer 222J (e.g., top region 226J of monolithic layer 222J) onto thefirst region 224J of monolithic layer 222J (e.g., bottom region 224J ofmonolithic layer 222J). The second piezoelectric axis orientation (e.g.,reverse axis orientation, e.g., upward pointing arrow) at second region226J of monolithic layer 222J (e.g., top region 226J of monolithic layer222J) corresponds to the second piezoelectric axis orientation (e.g.,reverse axis orientation, e.g., upward pointing arrow) of secondpiezoelectric layer 202J.

Similarly, as shown in FIG. 2D in a second detailed view 230J, withoutan interposer layer interposed between third layer of piezoelectricmaterial 203J and fourth layer of piezoelectric material 204J, the thirdand fourth piezoelectric layer 203J, 204J may be an additionalmonolithic layer 232J of piezoelectric material (e.g., Aluminum Nitride(AlN)) having first and second regions 234J, 236J. A central region ofadditional monolithic layer 232J of piezoelectric material (e.g.,Aluminum Nitride (AlN)) between first and second regions 234J, 236J maybe oxygen rich. The first region 234J of additional monolithic layer232J (e.g., bottom region 234J of additional monolithic layer 232J) hasthe first piezoelectric axis orientation (e.g., normal axis orientation)as representatively illustrated in second detailed view 230J using thedownward pointing arrow at first region 234J, (e.g., bottom region224J). This first piezoelectric axis orientation (e.g., normal axisorientation, e.g., downward pointing arrow) at first region 234J ofadditional monolithic layer 232J (e.g., bottom region 234J of additionalmonolithic layer 232J) corresponds to the first piezoelectric axisorientation (e.g., normal axis orientation, e.g., downward pointingarrow) of third piezoelectric layer 203J. The second region 236J ofadditional monolithic layer 232J (e.g., top region 236J of additionalmonolithic layer 232J) has the second piezoelectric axis orientation(e.g., reverse axis orientation) as representatively illustrated insecond detailed view 230J using the upward pointing arrow at secondregion 236J, (e.g., top region 236J). This second piezoelectric axisorientation (e.g., reverse axis orientation, e.g., upward pointingarrow) at second region 236J of additional monolithic layer 232J (e.g.,top region 236J of additional monolithic layer 232J) may be formed tooppose the first piezoelectric axis orientation (e.g., normal axisorientation, e.g., downward pointing arrow) at first region 234J ofadditional monolithic layer 232J (e.g., bottom region 234J of additionalmonolithic layer 232J) by adding gas (e.g., oxygen) to flip the axiswhile sputtering the second region 236J of additional monolithic layer232J (e.g., top region 236J of additional monolithic layer 232J) ontothe first region 234J of additional monolithic layer 232J (e.g., bottomregion 234J of additional monolithic layer 232J). The secondpiezoelectric axis orientation (e.g., reverse axis orientation, e.g.,upward pointing arrow) at second region 236J of additional monolithiclayer 232J (e.g., top region 236J of additional monolithic layer 232J)corresponds to the second piezoelectric axis orientation (e.g., reverseaxis orientation, e.g., upward pointing arrow) of fourth piezoelectriclayer 204J.

Similar to what was just discussed, without an interposer layerinterposed between fifth layer of piezoelectric material 205J and sixthlayer of piezoelectric material 206J, the fifth and sixth piezoelectriclayer 205J, 206J may be another additional monolithic layer ofpiezoelectric material (e.g., Aluminum Nitride (AlN)) having first andsecond regions. More generally, for example in FIG. 2D, where N is anodd positive integer, without an interposer layer interposed between Nthlayer of piezoelectric material and (N+1)th layer of piezoelectricmaterial, the Nth and (N+1)th piezoelectric layer may be an (N+1)/2thmonolithic layer of piezoelectric material (e.g., Aluminum Nitride(AlN)) having first and second regions. Accordingly, without aninterposer layer interposed between seventeenth layer of piezoelectricmaterial 217J and eighteenth layer of piezoelectric material 218J, theseventeenth and eighteenth piezoelectric layer 217J, 218J may be ninthmonolithic layer of piezoelectric material (e.g., Aluminum Nitride(AlN)) having first and second regions.

The first interposer layer 261J is shown in FIG. 2D as interposingbetween a first pair of opposing axis piezoelectric layers 201J, 202J,and a second pair of opposing axis piezoelectric layers 203J, 204J. Moregenerally, for example, where M is a positive integer, an Mth interposerlayer is shown in FIG. 2D as interposing between an Mth pair of opposingaxis piezoelectric layers and an (M+1)th pair of opposing axispiezoelectric layers. Accordingly, an eighth interposer layer is shownin FIG. 2D as interposing between an eighth pair of opposing axispiezoelectric layers 215J, 216J, and a ninth pair of opposing axispiezoelectric layers 217J, 218J. FIG. 2D shows an eighteen piezoelectriclayer alternating axis stack arrangement sandwiched between multilayermetal acoustic millimeter wave reflector top electrode 2015J andmultilayer metal acoustic millimeter wave reflector bottom electrode2013J. Etched edge region 253J (and laterally opposing etched edgeregion 254J) may extend through (e.g., entirely through, e.g., partiallythrough) the eighteen piezoelectric layer alternating axis stackarrangement and its interposer layers, and may extend through (e.g.,entirely through, e.g., partially through) multilayer metal acousticmillimeter wave reflector top electrode 2015J, and may extend through(e.g., entirely through, e.g., partially through) multilayer metalacoustic millimeter wave reflector bottom electrode 2013J. As shown inFIG. 2D, a first mesa structure corresponding to the stack of eighteenpiezoelectric material layers may extend laterally between (e.g., may beformed between) etched edge region 253J and laterally opposing etchededge region 254J. A second mesa structure corresponding to multilayermetal acoustic millimeter wave reflector bottom electrode 2013J mayextend laterally between (e.g., may be formed between) etched edgeregion 153J and laterally opposing etched edge region 154J. Third mesastructure corresponding to multilayer metal acoustic millimeter wavereflector top electrode 2015J may extend laterally between (e.g., may beformed between) etched edge region 153J and laterally opposing etchededge region 154J.

As mentioned previously herein, one or more (e.g., one or a pluralityof) interposer layers may be metal interposer layers. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may be dielectric interposer layers. Interposer layers may bemetal and/or dielectric interposer layers. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may be formed of different metal layers. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may be formed of different dielectric layers. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may comprise metal and dielectric for respective interposerlayers. Alternatively or additionally, one or more (e.g., one or aplurality of) interposer layers may be formed of different metal layers.For example, high acoustic impedance metal layer such as Tungsten (W) orMolybdenum (Mo) may (but need not) raise effective electromechanicalcoupling coefficient (Kt2) while subsequently deposited metal layer withhexagonal symmetry such as Titanium (Ti) may (but need not) facilitatehigher crystallographic quality of subsequently deposited piezoelectriclayer. Alternatively or additionally, one or more (e.g., one or aplurality of) interposer layers may be formed of different dielectriclayers. For example, high acoustic impedance dielectric layer such asHafnium Dioxide (HfO2) may (but need not) raise effectiveelectromechanical coupling coefficient (Kt2). Subsequently depositedamorphous dielectric layer such as Silicon Dioxide (SiO2) may (but neednot) facilitate compensating for temperature dependent frequency shifts.Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may comprise metal and dielectric for respectiveinterposer layers. For example, high acoustic impedance metal layer suchas Tungsten (W) or Molybdenum (Mo) may (but need not) raise effectiveelectromechanical coupling coefficient (Kt2) while subsequentlydeposited amorphous dielectric layer such as Silicon Dioxide (SiO2) may(but need not) facilitate compensating for temperature dependentfrequency shifts. For example, in FIG. 2D one or more of the interposerlayers (e.g., interposer layer 268J) may comprise metal and dielectricfor respective interposer layers. For example, detailed view 240J ofinterposer 268J shows interposer 268J as comprising metal sublayer 268JBover dielectric sublayer 268JA. For interposer 268J, example thicknessof metal sublayer 268JB may be approximately two hundred Angstroms (200A). For interposer 268J, example thickness of dielectric sublayer 268JAmay be approximately two hundred Angstroms (200 A). The secondpiezoelectric axis orientation (e.g., reverse axis orientation, e.g.,upward pointing arrow) at region 244J (e.g., bottom region 244J)corresponds to the second piezoelectric axis orientation (e.g., reverseaxis orientation, e.g., upward pointing arrow) of eighth piezoelectriclayer 208J. The first piezoelectric axis orientation (e.g., normal axisorientation, e.g., downward pointing arrow) at region 246J (e.g., topregion 246J) corresponds to the first piezoelectric axis orientation(e.g., normal orientation, e.g., downward pointing arrow) of ninthpiezoelectric layer 209J.

As discussed, interposer layers shown in FIG. 1A, and as explicitlyshown in the simplified diagrams of the various resonators shown inFIGS. 2A, 2B, 2C and 2D may be included and interposed between adjacentpiezoelectric layers in the various resonators. Such interposer layersmay laterally extend within the mesa structure of the stack ofpiezoelectric layers a full lateral extent of the stack, e.g., betweenthe etched edge region of the stack and the opposing etched edge regionof the stack. However, in some other alternative bulk acoustic waveresonator structures, interposer layers may be patterned duringfabrication of the interposer layers (e.g., patterned using masking andselective etching techniques during fabrication of the interposerlayers). Such patterned interposer layers need not extend a full lateralextent of the stack (e.g., need not laterally extend to any etched edgeregions of the stack.) For example, FIG. 2E shows another alternativebulk acoustic wave resonator structure 2001K, similar to bulk acousticwave resonator structure 2001J shown in FIG. 2D, but with differences.For example, in the alternative bulk acoustic wave resonator structure2001K shown in FIG. 2E, patterned interposer layers (e.g., firstpatterned interposer layer 261K) may be interposed between sequentialpairs of opposing axis piezoelectric layers (e.g., first patternedinterposer layer 295K may be interposed between a first pair of opposingaxis piezoelectric layers 201K, 202K, and a second pair of opposing axispiezoelectric layers 203K, 204K).

FIG. 2E shows an eighteen piezoelectric layer alternating axis stackarrangement having an active region of the bulk acoustic wave resonatorstructure 2001K sandwiched between overlap of multilayer metal acousticmillimeter wave reflector top electrode 2015IK and multilayer metalacoustic millimeter wave reflector bottom electrode 2013K. In FIG. 2E,patterned interposer layers (e.g., first patterned interposer layer261K) may be patterned to have extent limited to the active region ofthe bulk acoustic wave resonator structure 2001K sandwiched betweenoverlap of multilayer metal acoustic millimeter wave reflector topelectrode 2015K and multilayer metal acoustic millimeter wave reflectorbottom electrode 2013K. A planarization layer 256K at a limited extentof multilayer metal acoustic millimeter wave reflector bottom electrode2013K may facilitate fabrication of the eighteen piezoelectric layeralternating axis stack arrangement (e.g., stack of eighteenpiezoelectric layers 201K through 218K).

Patterning of interposer layers may be done in various combinations. Forexample, some interposer layers need not be patterned (e.g., may beunpatterned) within lateral extent of the stack of piezoelectric layers(e.g., some interposer layers may extend to full lateral extent of thestack of piezoelectric layers). For example, first interposer layer 261Jshown in FIG. 2D need not be patterned (e.g., may be unpatterned) withinlateral extent of the stack of piezoelectric layers (e.g., firstinterposer layer 261J may extend to full lateral extent of the stack ofpiezoelectric layers). For example, in FIG. 2D interposer layersinterposed between adjacent sequential pairs of normal axis and reverseaxis piezoelectric layers need not be patterned (e.g., may beunpatterned) within lateral extent of the stack of piezoelectric layers(e.g., interposer layers interposed between sequential pairs of normalaxis and reverse axis piezoelectric layers may extend to full lateralextent of the stack of piezoelectric layers). For example in FIG. 2D,first interposer layer 261J interposed between first sequential pair ofnormal axis and reverse axis piezoelectric layers 201J, 202J andadjacent second sequential pair of normal axis and reverse axispiezoelectric layers 203J, 204J need not be patterned within lateralextent of the stack of piezoelectric layers (e.g., first interposerlayer 261J may extend to full lateral extent of the stack ofpiezoelectric layers). In contrast to these unpatterned interposerlayers (e.g., in contrast to unpatterned interposer layer 261J) as shownin FIG. 2D, in FIG. 2E patterned interposer layers (e.g., firstpatterned interposer layer 261K) may be patterned, for example, to haveextent limited to the active region of the bulk acoustic wave resonatorstructure 2001K shown in FIG. 2E.

FIGS. 3A through 3E illustrate example integrated circuit structuresused to form the example bulk acoustic wave resonator structure of FIG.1A. As shown in FIG. 3A, magnetron sputtering may sequentially depositlayers on silicon substrate 101. Initially, a seed layer 103 of suitablematerial (e.g., aluminum nitride (AlN), e.g., silicon dioxide (SiO₂),e.g., aluminum oxide (Al₂O₃), e.g., silicon nitride (Si₃N₄), e.g.,amorphous silicon (a-Si), e.g., silicon carbide (SiC)) may be deposited,for example, by sputtering from a respective target (e.g., from analuminum, silicon, or silicon carbide target). The seed layer may have alayer thickness in a range from approximately one hundred Angstroms (100A) to approximately one micron (1 um). Next, successive pairs ofalternating layers of high acoustic impedance metal and low acousticimpedance metal may be deposited by alternating sputtering from targetsof high acoustic impedance metal and low acoustic impedance metal. Forexample, sputtering targets of high acoustic impedance metal such asMolybdenum or Tungsten may be used for sputtering the high acousticimpedance metal layers, and sputtering targets of low acoustic impedancemetal such as Aluminum or Titanium may be used for sputtering the lowacoustic impedance metal layers. For example, the fourth pair of bottommetal electrode layers, 133, 131, may be deposited by sputtering thehigh acoustic impedance metal for a first bottom metal electrode layer133 of the pair on the seed layer 103, and then sputtering the lowacoustic impedance metal for a second bottom metal electrode layer 131of the pair on the first layer 133 of the pair. Similarly, the thirdpair of bottom metal electrode layers, 129, 127, may then be depositedby sequentially sputtering from the high acoustic impedance metal targetand the low acoustic impedance metal target. Similarly, the second pairof bottom metal electrodes 125, 123, may then be deposited bysequentially sputtering from the high acoustic impedance metal targetand the low acoustic impedance metal target. Similarly, the first pairof bottom metal electrodes 121, 119, may then be deposited bysequentially sputtering from the high acoustic impedance metal targetand the low acoustic impedance metal target. Respective layerthicknesses of bottom metal electrode layers of the first, second, thirdand fourth pairs 119, 121, 123, 125, 127, 129, 131, 133 may correspondto approximately a quarter wavelength (e.g., a quarter of an acousticwavelength) of the resonant frequency at the resonator (e.g., respectivelayer thickness of about six hundred Angstroms (660 A) for the example24 GHz resonator.) Initial bottom electrode layer 119 may then bedeposited by sputtering from the high acoustic impedance metal target.Thickness of the initial bottom electrode layer may be, for example,about an eighth wavelength (e.g., an eighth of an acoustic wavelength)of the resonant frequency of the resonator (e.g., layer thickness ofabout three hundred Angstroms (300 A) for the example 24 GHz resonator.)

A stack of four layers of piezoelectric material, for example, fourlayers of Aluminum Nitride (AlN) having the wurtzite structure may bedeposited by sputtering. For example, bottom piezoelectric layer 105,first middle piezoelectric layer 107, second middle piezoelectric layer109, and top piezoelectric layer 111 may be deposited by sputtering. Thefour layers of piezoelectric material in the stack 104, may have thealternating axis arrangement in the respective stack 104. For examplethe bottom piezoelectric layer 105 may be sputter deposited to have thenormal axis orientation, which is depicted in FIG. 3A using the downwarddirected arrow. The first middle piezoelectric layer 107 may be sputterdeposited to have the reverse axis orientation, which is depicted in theFIG. 3A using the upward directed arrow. The second middle piezoelectriclayer 109 may have the normal axis orientation, which is depicted in theFIG. 3A using the downward directed arrow. The top piezoelectric layermay have the reverse axis orientation, which is depicted in the FIG. 3Ausing the upward directed arrow. As mentioned previously herein,polycrystalline thin film AlN may be grown in the crystallographicc-axis negative polarization, or normal axis orientation perpendicularrelative to the substrate surface using reactive magnetron sputtering ofthe Aluminum target in the nitrogen atmosphere. As was discussed ingreater detail previously herein, changing sputtering conditions, forexample by adding oxygen, may reverse the axis to a crystallographicc-axis positive polarization, or reverse axis, orientation perpendicularrelative to the substrate surface.

Interposer layers may be sputtered between sputtering of piezoelectriclayers, so as to be sandwiched between piezoelectric layers of thestack. For example, first interposer layer 159, may sputtered betweensputtering of bottom piezoelectric layer 105, and the first middlepiezoelectric layer 107, so as to be sandwiched between the bottompiezoelectric layer 105, and the first middle piezoelectric layer 107.For example, second interposer layer 161 may be sputtered betweensputtering first middle piezoelectric layer 107 and the second middlepiezoelectric layer 109 so as to be sandwiched between the first middlepiezoelectric layer 107, and the second middle piezoelectric layer 109.For example, third interposer layer 163, may be sputtered betweensputtering of second middle piezoelectric layer 109 and the toppiezoelectric layer 111 so as to be sandwiched between the second middlepiezoelectric layer 109 and the top piezoelectric layer 111.

As discussed previously, one or more of the interposer layers (e.g.,interposer layers 159, 161, 163) may be metal interposer layers, e.g.,high acoustic impedance metal interposer layers, e.g., Molybdenum metalinterposer layers. These may be deposited by sputtering from a metaltarget. As discussed previously, one or more of the interposer layers(e.g., interposer layers 159, 161, 163) may be dielectric interposerlayers, e.g., silicon dioxide interposer layers. These may be depositedby reactive sputtering from a Silicon target in an oxygen atmosphere.Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may be formed of different metal layers. Alternativelyor additionally, one or more (e.g., one or a plurality of) interposerlayers may be formed of different dielectric layers. Alternatively oradditionally, one or more of the interposer layers (e.g., interposerlayers 159, 161, 163) may be metal and dielectric. Sputtering thicknessof interposer layers may be as discussed previously herein. Interposerlayers may facilitate sputter deposition of piezoelectric layers. Forexample, initial sputter deposition of second interposer layer 166 onreverse axis first middle piezoelectric layer 107 may facilitatesubsequent sputter deposition of normal axis second middle piezoelectriclayer 109.

Initial top electrode layer 135 may be deposited on the toppiezoelectric layer 111 by sputtering from the high acoustic impedancemetal target. Thickness of the initial top electrode layer may be, forexample, about an eighth wavelength (e.g., an eighth of an acousticwavelength) of the resonant frequency of the resonator (e.g., layerthickness of about three hundred Angstroms (300 A) for the example 24GHz resonator.) The first pair of top metal electrode layers, 137, 139,may then be deposited by sputtering the low acoustic impedance metal fora first top metal electrode layer 137 of the pair, and then sputteringthe high acoustic impedance metal for a second top metal electrode layer139 of the pair on the first layer 137 of the pair. Layer thicknesses oftop metal electrode layers of the first pair 137, 139 may correspond toapproximately a quarter wavelength (e.g., a quarter acoustic wavelength)of the resonant frequency of the resonator (e.g., respective layerthickness of about six hundred Angstroms (600 A) for the example 24 GHzresonator.) The optional mass load layer 155 may be sputtered from ahigh acoustic impedance metal target onto the second top metal electrodelayer 139 of the pair. Thickness of the optional mass load layer may beas discussed previously herein. The mass load layer 155 may be anadditional mass layer to increase electrode layer mass, so as tofacilitate the preselected frequency compensation down in frequency(e.g., compensate to decrease resonant frequency). Alternatively, themass load layer 155 may be a mass load reduction layer, e.g., ion milledmass load reduction layer 155, to decrease electrode layer mass, so asto facilitate the preselected frequency compensation up in frequency(e.g., compensate to increase resonant frequency). Accordingly, in suchcase, in FIG. 3A mass load reduction layer 155 may representativelyillustrate, for example, an ion milled region of the second member 139of the first pair of electrodes 137, 139 (e.g., ion milled region ofhigh acoustic impedance metal electrode 139).

The plurality of lateral features 157 (e.g., patterned layer 157) may beformed by sputtering a layer of additional mass loading having a layerthickness as discussed previously herein. The plurality of lateralfeatures 157 (e.g., patterned layer 157) may be made by patterning thelayer of additional mass loading after it is deposited by sputtering.The patterning may done by photolithographic masking, layer etching, andmask removal. Initial sputtering may be sputtering of a metal layer ofadditional mass loading from a metal target (e.g., a target of Tungsten(W), Molybdenum (Mo), Titanium (Ti), or Aluminum (Al)). In alternativeexamples, the plurality of lateral features 157 may be made of apatterned dielectric layer (e.g., a patterned layer of Silicon Nitride(SiN), Silicon Dioxide (SiO2) or Silicon Carbide (SiC)). For exampleSilicon Nitride, and Silicon Dioxide may be deposited by reactivemagnetron sputtering from a silicon target in an appropriate atmosphere,for example Nitrogen, Oxygen or Carbon Dioxide. Silicon Carbide may besputtered from a Silicon Carbide target.

Once the plurality of lateral features 157 have been patterned (e.g.,patterned layer 157) as shown in FIG. 3A, sputter deposition ofsuccessive additional pairs of alternating layers of high acousticimpedance metal and low acoustic impedance metal may continue as shownin FIG. 3B by alternating sputtering from targets of high acousticimpedance metal and low acoustic impedance metal. For example,sputtering targets of high acoustic impedance metal such as Molybdenumor Tungsten may be used for sputtering the high acoustic impedance metallayers, and sputtering targets of low acoustic impedance metal such asAluminum or Titanium may be used for sputtering the low acousticimpedance metal layers. For example, the second pair of top metalelectrode layers, 141, 143, may be deposited by sputtering the lowacoustic impedance metal for a first bottom metal electrode layer 141 ofthe pair on the plurality of lateral features 157, and then sputteringthe high acoustic impedance metal for a second top metal electrode layer143 of the pair on the first layer 141 of the pair. Similarly, the thirdpair of top metal electrode layers, 145, 147, may then be deposited bysequentially sputtering from the low acoustic impedance metal target andthe high acoustic impedance metal target. Similarly, the fourth pair oftop metal electrodes 149, 151, may then be deposited by sequentiallysputtering from the low acoustic impedance metal target and the highacoustic impedance metal target. Respective layer thicknesses of topmetal electrode layers of the first, second, third and fourth pairs 137,139, 141, 143, 145, 147, 149, 151 may correspond to approximately aquarter wavelength (e.g., a quarter acoustic wavelength) at the resonantfrequency of the resonator (e.g., respective layer thickness of aboutsix hundred Angstroms (600 A) for the example 24 GHz resonator.)

As mentioned previously, and as shown in FIG. 3B, after the lateralfeatures 157 are formed, (e.g., patterned layer 157), they may functionas a step feature template, so that subsequent top metal electrodelayers formed on top of the lateral features 157 may retain steppatterns imposed by step features of the lateral features 157. Forexample, the second pair of top metal electrode layers 141, 143, thethird pair of top metal electrode layers 145, 147, and the fourth pairof top metal electrodes 149, 151, may retain step patterns imposed bystep features of the lateral features 157.

After depositing layers of the fourth pair of top metal electrodes 149,151 as shown in FIG. 3B, suitable photolithographic masking and etchingmay be used to form a first portion of etched edge region 153C for thetop acoustic reflector 115 as shown in FIG. 3C. A notional heavy dashedline is used in FIG. 3C depicting the first portion of etched edgeregion 153C associated with the top acoustic reflector 115. The firstportion of etched edge region 153C may extend along the thicknessdimension T25 of the top acoustic reflector 115. The first portionetched edge region 153C may extend through (e.g., entirely through orpartially through) the top acoustic reflector 115. The first portion ofthe etched edge region 153C may extend through (e.g., entirely throughor partially through) the initial top metal electrode layer 135. Thefirst portion of the etched edge region 153C may extend through (e.g.,entirely through or partially through) the first pair of top metalelectrode layers 137, 139. The first portion of the etched edge region153C may extend through (e.g., entirely through or partially through)the optional mass load layer 155. The first portion of the etched edgeregion 153C may extend through (e.g., entirely through or partiallythrough) at least one of the lateral features 157 (e.g., throughpatterned layer 157). The first portion of etched edge region 153C mayextend through (e.g., entirely through or partially through) the secondpair of top metal electrode layers, 141,143. The first portion etchededge region 153C may extend through (e.g., entirely through or partiallythrough) the third pair of top metal electrode layers, 145, 147. Thefirst portion of etched edge region 153C may extend through (e.g.,entirely through or partially through) the fourth pair of top metalelectrode layers, 149, 151. Just as suitable photolithographic maskingand etching may be used to form the first portion of etched edge region153C at a lateral extremity the top acoustic reflector 115 as shown inFIG. 3C, such suitable photolithographic masking and etching maylikewise be used to form another first portion of a laterally opposingetched edge region 154C at an opposing lateral extremity the topacoustic reflector 115, e.g., arranged laterally opposing or oppositefrom the first portion of etched edge region 153C, as shown in FIG. 3C.The another first portion of the laterally opposing etched edge region154C may extend through (e.g., entirely through or partially through)the opposing lateral extremity of the top acoustic reflector 115, e.g.,arranged laterally opposing or opposite from the first portion of etchededge region 153C, as shown in FIG. 3C. The mesa structure (e.g., thirdmesa structure) corresponding to the top acoustic reflector 115 mayextend laterally between (e.g., may be formed between) etched edgeregion 153C and laterally opposing etched edge region 154C. Dry etchingmay be used, e.g., reactive ion etching may be used to etch thematerials of the top acoustic reflector. Chlorine based reactive ionetch may be used to etch Aluminum, in cases where Aluminum is used inthe top acoustic reflector. Fluorine based reactive ion etch may be usedto etch Tungsten (W), Molybdenum (Mo), Titanium (Ti), Silicon Nitride(SiN), Silicon Dioxide (SiO2) and/or Silicon Carbide (SiC) in caseswhere these materials are used in the top acoustic reflector.

After etching to form the first portion of etched edge region 153C fortop acoustic reflector 115 as shown in FIG. 3C, additional suitablephotolithographic masking and etching may be used to form elongatedportion of etched edge region 153D for top acoustic reflector 115 andfor the stack 104 of four piezoelectric layers 105, 107, 109, 111 asshown in FIG. 3D. A notional heavy dashed line is used in FIG. 3Ddepicting the elongated portion of etched edge region 153D associatedwith the stack 104 of four piezoelectric layers 105, 107, 109, 111 andwith the top acoustic reflector 115. Accordingly, the elongated portionof etched edge region 153D shown in FIG. 3D may extend through (e.g.,entirely through or partially through) the fourth pair of top metalelectrode layers, 149, 151, the third pair of top metal electrodelayers, 145, 147, the second pair of top metal electrode layers,141,143, at least one of the lateral features 157 (e.g., throughpatterned layer 157), the optional mass load layer 155, the first pairof top metal electrode layers 137, 139 and the initial top metalelectrode layer 135 of the top acoustic reflector 115. The elongatedportion of etched edge region 153D may extend through (e.g., entirelythrough or partially through) the stack 104 of four piezoelectric layers105, 107, 109, 111. The elongated portion of etched edge region 153D mayextend through (e.g., entirely through or partially through) the firstpiezoelectric layer, 105, e.g., having the normal axis orientation,first interposer layer 159, first middle piezoelectric layer, 107, e.g.,having the reverse axis orientation, second interposer layer 161, secondmiddle interposer layer, 109, e.g., having the normal axis orientation,third interposer layer 163, and top piezoelectric layer 111, e.g.,having the reverse axis orientation. The elongated portion of etchededge region 153D may extend along the thickness dimension T25 of the topacoustic reflector 115. The elongated portion of etched edge region 153Dmay extend along the thickness dimension T27 of the stack 104 of fourpiezoelectric layers 105, 107, 109, 111. Just as suitablephotolithographic masking and etching may be used to form the elongatedportion of etched edge region 153D at the lateral extremity the topacoustic reflector 115 and at a lateral extremity of the stack 104 offour piezoelectric layers 105, 107, 109, 111 as shown in FIG. 3D, suchsuitable photolithographic masking and etching may likewise be used toform another elongated portion of the laterally opposing etched edgeregion 154D at the opposing lateral extremity the top acoustic reflector115 and the stack 104 of four piezoelectric layers 105, 107, 109, 111,e.g., arranged laterally opposing or opposite from the elongated portionof etched edge region 153D, as shown in FIG. 3D. The another elongatedportion of the laterally opposing etched edge region 154D may extendthrough (e.g., entirely through or partially through) the opposinglateral extremity of the top acoustic reflector 115 and the stack offour piezoelectric layers 105, 107, 109, 111, e.g., arranged laterallyopposing or opposite from the elongated portion of etched edge region153D, as shown in FIG. 3D. The mesa structure (e.g., third mesastructure) corresponding to the top acoustic reflector 115 may extendlaterally between (e.g., may be formed between) etched edge region 153Dand laterally opposing etched edge region 154D. The mesa structure(e.g., first mesa structure) corresponding to stack 104 of the examplefour piezoelectric layers may extend laterally between (e.g., may beformed between) etched edge region 153D and laterally opposing etchededge region 154D. Dry etching may be used, e.g., reactive ion etchingmay be used to etch the materials of the stack 104 of four piezoelectriclayers 105, 107, 109, 111 and any interposer layers. For example,Chlorine based reactive ion etch may be used to etch Aluminum Nitridepiezoelectric layers. For example, Fluorine based reactive ion etch maybe used to etch Tungsten (W), Molybdenum (Mo), Titanium (Ti), SiliconNitride (SiN), Silicon Dioxide (SiO2) and/or Silicon Carbide (SiC) incases where these materials are used in interposer layers.

After etching to form the elongated portion of etched edge region 153Dfor top acoustic reflector 115 and the stack 104 of four piezoelectriclayers 105, 107, 109, 111 as shown in FIG. 3D, further additionalsuitable photolithographic masking and etching may be used to formetched edge region 153D for top acoustic reflector 115 and for the stack104 of four piezoelectric layers 105, 107, 109, 111 and for bottomacoustic reflector 113 as shown in FIG. 3E. The notional heavy dashedline is used in FIG. 3E depicting the etched edge region 153 associatedwith the stack 104 of four piezoelectric layers 105, 107, 109, 111 andwith the top acoustic reflector 115 and with the bottom acousticreflector 113. The etched edge region 153 may extend along the thicknessdimension T25 of the top acoustic reflector 115. The etched edge region153 may extend along the thickness dimension T27 of the stack 104 offour piezoelectric layers 105, 107, 109, 111. The etched edge region 153may extend along the thickness dimension T23 of the bottom acousticreflector 113. Just as suitable photolithographic masking and etchingmay be used to form the etched edge region 153 at the lateral extremitythe top acoustic reflector 115 and at the lateral extremity of the stack104 of four piezoelectric layers 105, 107, 109, 111 and at a lateralextremity of the bottom acoustic reflector 113 as shown in FIG. 3E, suchsuitable photolithographic masking and etching may likewise be used toform another laterally opposing etched edge region 154 at the opposinglateral extremity of the top acoustic reflector 115 and the stack 104 offour piezoelectric layers 105, 107, 109, 111, and the bottom acousticreflector 113, e.g., arranged laterally opposing or opposite from theetched edge region 153, as shown in FIG. 3E. The laterally opposingetched edge region 154 may extend through (e.g., entirely through orpartially through) the opposing lateral extremity of the top acousticreflector 115 and the stack of four piezoelectric layers 105, 107, 109,111, and the bottom acoustic reflector 113 e.g., arranged laterallyopposing or opposite from the etched edge region 153, as shown in FIG.3E.

After the foregoing etching to form the etched edge region 153 and thelaterally opposing etched edge region 154 of the resonator 100 shown inFIG. 3E, a planarization layer 165 may be deposited. A suitableplanarization material (e.g., Silicon Dioxide (SiO2), Hafnium Dioxide(HfO2), Polyimide, or BenzoCyclobutene (BCB)). These materials may bedeposited by suitable methods, for example, chemical vapor deposition,standard or reactive magnetron sputtering (e.g., in cases of SiO2 orHfO2) or spin coating (e.g., in cases of Polyimide or BenzoCyclobutene(BCB)). An isolation layer 167 may also be deposited over theplanarization layer 165. A suitable low dielectric constant (low-k), lowacoustic impedance (low-Za) material may be used for the isolation layer167, for example polyimide, or BenzoCyclobutene (BCB). These materialsmay be deposited by suitable methods, for example, chemical vapordeposition, standard or reactive magnetron sputtering or spin coating.After planarization layer 165 and the isolation layer 167 have beendeposited, additional procedures of photolithographic masking, layeretching, and mask removal may be done to form a pair of etchedacceptance locations 183A, 183B for electrical interconnections.Reactive ion etching or inductively coupled plasma etching with a gasmixture of argon, oxygen and a fluorine containing gas such astetrafluoromethane (CF4) or Sulfur hexafluoride (SF6) may be used toetch through the isolation layer 167 and the planarization layer 165 toform the pair of etched acceptance locations 183A, 183B for electricalinterconnections. Photolithographic masking, sputter deposition, andmask removal may then be used form electrical interconnects in the pairof etched acceptance locations 183A, 183B shown in FIG. 3E, so as toprovide for the bottom electrical interconnect 169 and top electricalinterconnect 171 that are shown explicitly in FIG. 1A. A suitablematerial, for example Gold (Au) may be used for the bottom electricalinterconnect 169 and top electrical interconnect 171.

FIGS. 4A through 4G show alternative example bulk acoustic waveresonators 400A through 400G to the example bulk acoustic wave resonator100A shown in FIG. 1A. For example, the bulk acoustic wave resonator400A, 400E shown in FIG. 4A, 4E may have a cavity 483A, 483E, e.g., anair cavity 483A, 483E, e.g., extending into substrate 401A, 401E, e.g.,extending into silicon substrate 401A, 401E, e.g., arranged below bottomacoustic reflector 413A, 413E. The cavity 483A, 483E may be formed usingtechniques known to those with ordinary skill in the art. For example,the cavity 483A,483E may be formed by initial photolithographic maskingand etching of the substrate 401A, 401E (e.g., silicon substrate 401A,401E), and deposition of a sacrificial material (e.g., phosphosilicateglass (PSG)). The phosphosilicate glass (PSG) may comprise 8%phosphorous and 92% silicon dioxide. The resonator 400A, 400E may beformed over the sacrificial material (e.g., phosphosilicate glass(PSG)). The sacrificial material may then be selectively etched awaybeneath the resonator 400A, 400E, leaving cavity 483A, 483E beneath theresonator 400A, 400E. For example phosphosilicate glass (PSG)sacrificial material may be selectively etched away by hydrofluoric acidbeneath the resonator 400A, 400E, leaving cavity 483A, 483E beneath theresonator 400A, 400E. The cavity 483A, 483E may, but need not, bearranged to provide acoustic isolation of the structures, e.g., bottomacoustic reflector 413A, 413E, e.g., stack 404A, 404E of piezoelectriclayers, e.g., resonator 400A, 400E from the substrate 401A, 401E.

Similarly, in FIGS. 4B, 4C, 4F and 4G, a via 485B, 485C, 485F, 485G(e.g., through silicon via 485B, 485F, e.g., through silicon carbide via485C, 485G) may, but need not, be arranged to provide acoustic isolationof the structures, e.g., bottom acoustic reflector 413B, 413C, 413F,413G, e.g., stack 404B, 404C, 404F, 404G, of piezoelectric layers, e.g.,resonator 400B, 400C, 400F, 400G from the substrate 401B, 401C, 401F,401G. The via 485B, 485C, 485F, 485G (e.g., through silicon via 485B,485F, e.g., through silicon carbide via 485C, 485G) may be formed usingtechniques (e.g., using photolithographic masking and etchingtechniques) known to those with ordinary skill in the art. For example,in FIGS. 4B and 4F, backside photolithographic masking and etchingtechniques may be used to form the through silicon via 485B, 485F, andan additional passivation layer 487B, 487F may be deposited, after theresonator 400B, 400F is formed. For example, in FIGS. 4C and 4G,backside photolithographic masking and etching techniques may be used toform the through silicon carbide via 485C, 485G, after the top acousticreflector 415C, 415G and stack 404C, 404G of piezoelectric layers areformed. In FIGS. 4C and 4G, after the through silicon carbide via 485C,485G, is formed, backside photolithographic masking and depositiontechniques may be used to form bottom acoustic reflector 413C, 413G, andadditional passivation layer 487C, 487G.

In FIGS. 4A, 4B, 4C, 4E, 4F, 4G, bottom acoustic reflector 413A, 413B,413C, 413E, 413F, 413G, may include the acoustically reflective bottomelectrode stack of the plurality of bottom metal electrode layers, inwhich thicknesses of the bottom metal electrode layers may be related towavelength (e.g., acoustic wavelength) at the main resonant frequency ofthe example resonator 400A, 400B, 400C, 400E, 400F, 400G. As mentionedpreviously herein, the layer thickness of the initial bottom metalelectrode layer 417A, 417B, 417C, 417E, 417F, 417G, may be about oneeighth of a wavelength (e.g., one eighth acoustic wavelength) at themain resonant frequency of the example resonator 400A. Respective layerthicknesses, (e.g., T01 through T04, explicitly shown in FIGS. 4A, 4B,4C) for members of the pairs of bottom metal electrode layers may beabout one quarter of the wavelength (e.g., one quarter acousticwavelength) at the main resonant frequency of the example resonators400A, 400B, 400C, 400E, 400F, 400G. Relatively speaking, in variousalternative designs of the example resonators 400A, 400B, 400C, 400E,400F, 400G, for relatively lower main resonant frequencies (e.g., fiveGigahertz (5 GHz)) and having corresponding relatively longerwavelengths (e.g., longer acoustic wavelengths), may have relativelythicker bottom metal electrode layers in comparison to other alternativedesigns of the example resonators 400A, 400B, 400C, 400E, 400F, 400G,for relatively higher main resonant frequencies (e.g., twenty-fourGigahertz (24 GHz)). There may be corresponding longer etching times toform, e.g., etch through, the relatively thicker bottom metal electrodelayers in designs of the example resonator 400A, 400B, 400C, 400E, 400F,400G, for relatively lower main resonant frequencies (e.g., fiveGigahertz (5 GHz)). Accordingly, in designs of the example resonators400A, 400B, 400C, 400E, 400F, 400G, for relatively lower main resonantfrequencies (e.g., five Gigahertz (5 GHz)) having the relatively thickerbottom metal electrode layers, there may (but need not) be an advantagein etching time in having a relatively fewer number (e.g., five (5)) ofbottom metal electrode layers, shown in 4A, 4B, 4C, 4E, 4F, 4G, incomparison to a relatively larger number (e.g., nine (9)) of bottommetal electrode layers, shown in FIG. 1A and in FIG. 4D. The relativelylarger number (e.g., nine (9)) of bottom metal electrode layers, shownin FIG. 1A and in FIG. 4D may (but need not) provide for relativelygreater acoustic isolation than the relatively fewer number (e.g., five(5)) of bottom metal electrode layers. However, in FIGS. 4A and 4E thecavity 483A, 483E, (e.g., air cavity 483A, 483E) may (but need not) bearranged to provide acoustic isolation enhancement relative to somedesigns without the cavity 483A, 483E. Similarly, in FIGS. 4B, 4C, 4F,4G, the via 483B, 483C, 483F, 483G, (e.g., through silicon via 485B,485F, e.g., through silicon carbide via 485C, 485G) may (but need not)be arranged to provide acoustic isolation enhancement relative to somedesigns without the via 483B, 483C, 483F, 483G.

In FIGS. 4A and 4E, the cavity 483A, 483E may (but need not) be arrangedto compensate for relatively lesser acoustic isolation of the relativelyfewer number (e.g., five (5)) of bottom metal electrode layers. In FIGS.4A and 4E, the cavity 483A, 483E may (but need not) be arranged toprovide acoustic isolation benefits, while retaining possible electricalconductivity improvements and etching time benefits of the relativelyfewer number (e.g., five (5)) of bottom metal electrode layers, e.g.,particularly in designs of the example resonator 400A, 400E, forrelatively lower main resonant frequencies (e.g., five Gigahertz (5GHz)). Similarly, in FIGS. 4B, 4C, 4F, 4G, the via 483B, 483C, 483F,483G, may (but need not) be arranged to compensate for relatively lesseracoustic isolation of the relatively fewer number (e.g., five (5)) ofbottom metal electrode layers. In FIGS. 4B, 4C, 4F, 4G, the via 483B,483C, 483F, 483G, may (but need not) be arranged to provide acousticisolation benefits, while retaining possible electrical conductivityimprovement benefits and etching time benefits of the relatively fewernumber (e.g., five (5)) of bottom metal electrode layers, e.g.,particularly in designs of the example resonator 400B, 400C, 400F, 400G,for relatively lower main resonant frequencies (e.g., five Gigahertz (5GHz), e.g., below six Gigahertz (6 GHz), e.g., below five Gigahertz (5GHz)).

FIGS. 4D through 4G show alternative example bulk acoustic waveresonators 400D through 400G to the example bulk acoustic wave resonator100A shown in FIG. 1A, in which the top acoustic reflector, 415D through415G, may comprise a lateral connection portion, 489D through 489G,(e.g., bridge portion, 489D through 489G), of the top acousticreflector, 415D through 415G. A gap, 491D through 491G, may be formedbeneath the lateral connection portion, 489D through 489G, (e.g., bridgeportion, 489D through 489G), of the top acoustic reflector 415D through415G. The gap, 491D through 491G, may be arranged adjacent to the etchededge region, 453D through 453G, of the example resonators 400D through400G.

For example, the gap, 491D through 491G, may be arranged adjacent towhere the etched edge region, 453D through 453G, extends through (e.g.,extends entirely through or extends partially through) the stack 404Dthrough 404G, of piezoelectric layers, for example along the thicknessdimension T27 of the stack 404D through 404G. For example, the gap, 491Dthrough 491G, may be arranged adjacent to where the etched edge region,453D through 453G, extends through (e.g., extends entirely through orextends partially through) the bottom piezoelectric layer 405D through405G. For example, the gap, 491D through 491G, may be arranged adjacentto where the etched edge region, 453D through 453G, extends through(e.g., extends entirely through or extends partially through) the bottompiezoelectric layer 405D through 405G. For example, the gap, 491Dthrough 491G, may be arranged adjacent to where the etched edge region,453D through 453G, extends through (e.g., extends entirely through orextends partially through) the first middle piezoelectric layer 407Dthrough 407G. For example, the gap, 491D through 491G, may be arrangedadjacent to where the etched edge region, 453D through 453G, extendsthrough (e.g., extends entirely through or extends partially through)the second middle piezoelectric layer 409D through 409G. For example,the gap, 491D through 491G, may be arranged adjacent to where the etchededge region, 453D through 453G, extends through (e.g., extends entirelythrough or extends partially through) the top piezoelectric layer 411Dthrough 411G. For example, the gap, 491D through 491G, may be arrangedadjacent to where the etched edge region, 453D through 453G, extendsthrough (e.g., extends entirely through or extends partially through)one or more interposer layers (e.g., first interposer layer, 495Dthrough 459G, second interposer layer, 461D through 461G, thirdinterposer layer 411D through 411G).

For example, as shown in FIGS. 4D through 4G, the gap, 491D through491G, may be arranged adjacent to where the etched edge region, 453Dthrough 453G, extends through (e.g., extends partially through) the topacoustic reflector 415D through 415G, for example partially along thethickness dimension T25 of the top acoustic reflector 415D through 415G.For example, the gap, 491D through 491G, may be arranged adjacent towhere the etched edge region, 453D through 453G, extends through (e.g.,extends entirely through or extends partially through) the initial topelectrode layer 435D through 435G. For example, the gap, 491D through491G, may be arranged adjacent to where the etched edge region, 453Dthrough 453G, extends through (e.g., extends entirely through or extendspartially through) the first member, 437D through 437G, of the firstpair of top electrode layers, 437D through 437G, 439D through 439G.

For example, as shown in FIGS. 4D through 4F, the gap, 491D through491F, may be arranged adjacent to where the etched edge region, 453Dthrough 453F, extends through (e.g., extends entirely through or extendspartially through) the bottom acoustic reflector 413D through 413F, forexample along the thickness dimension T23 of the bottom acousticreflector 413D through 413F. For example, the gap, 491D through 491F,may be arranged adjacent to where the etched edge region, 453D through453F, extends through (e.g., extends entirely through or extendspartially through) the initial bottom electrode layer 417D through 417F.For example, the gap, 491D through 491F, may be arranged adjacent towhere the etched edge region, 453D through 453F, extends through (e.g.,extends entirely through or extends partially through) the first pair ofbottom electrode layers, 419D through 419F, 421D through 421F. Forexample, the gap, 491D through 491F, may be arranged adjacent to wherethe etched edge region, 453D through 453F, extends through (e.g.,extends entirely through or extends partially through) the second pairof bottom electrode layers, 423D through 423F, 425D through 425F. Forexample, as shown in FIGS. 4D through 4F, the etched edge region, 453Dthrough 453F, may extend through (e.g., entirely through or partiallythrough) the bottom acoustic reflector, 413D through 413F, and through(e.g., entirely through or partially through) one or more of thepiezoelectric layers, 405D through 405F, 407D through 407F, 409D through409F, 411D through 411F, to the lateral connection portion, 489D through489G, (e.g., to the bridge portion, 489D through 489G), of the topacoustic reflector, 415D through 415F.

As shown in FIGS. 4D-4G, lateral connection portion, 489D through 489G,(e.g., bridge portion, 489D through 489G), of top acoustic reflector,415D through 415G, may be a multilayer lateral connection portion, 415Dthrough 415G, (e.g., a multilayer metal bridge portion, 415D through415G, comprising differing metals, e.g., metals having differingacoustic impedances.) For example, lateral connection portion, 489Dthrough 489G, (e.g., bridge portion, 489D through 489G), of top acousticreflector, 415D through 415G, may comprise the second member, 439Dthrough 439G, (e.g., comprising the relatively high acoustic impedancemetal) of the first pair of top electrode layers, 437D through 437G,439D through 439G. For example, lateral connection portion, 489D through489G, (e.g., bridge portion, 489D through 489G), of top acousticreflector, 415D through 415G, may comprise the second pair of topelectrode layers, 441D through 441G, 443D through 443G.

Gap 491D-491G may be an air gap 491D-491G, or may be filled with arelatively low acoustic impedance material (e.g., BenzoCyclobutene(BCB)), which may be deposited using various techniques known to thosewith skill in the art. Gap 491D-491G may be formed by depositing asacrificial material (e.g., phosphosilicate glass (PSG)) after theetched edge region, 453D through 453G, is formed. The lateral connectionportion, 489D through 489G, (e.g., bridge portion, 489D through 489G),of top acoustic reflector, 415D through 415G, may then be deposited(e.g., sputtered) over the sacrificial material. The sacrificialmaterial may then be selectively etched away beneath the lateralconnection portion, 489D through 489G, (e.g., e.g., beneath the bridgeportion, 489D through 489G), of top acoustic reflector, 415D through415G, leaving gap 491D-491G beneath the lateral connection portion, 489Dthrough 489G, (e.g., beneath the bridge portion, 489D through 489G). Forexample the phosphosilicate glass (PSG) sacrificial material may beselectively etched away by hydrofluoric acid beneath the lateralconnection portion, 489D through 489G, (e.g., beneath the bridgeportion, 489D through 489G), of top acoustic reflector, 415D through415G, leaving gap 491D-491G beneath the lateral connection portion, 489Dthrough 489G, (e.g., beneath the bridge portion, 489D through 489G).

Although in various example resonators, 100A, 400A, 400B, 400D, 400E,400F, polycrystalline piezoelectric layers (e.g., polycrystallineAluminum Nitride (AlN)) may be deposited (e.g., by sputtering), in otherexample resonators 400C, 400G, alternative single crystal or near singlecrystal piezoelectric layers (e.g., single/near single crystal AluminumNitride (AlN)) may be deposited (e.g., by metal organic chemical vapordeposition (MOCVD)). Normal axis piezoelectric layers (e.g., normal axisAluminum Nitride (AlN) piezoelectric layers) may be deposited by MOCVDusing techniques known to those with skill in the art. As discussedpreviously herein, the interposer layers may be deposited by sputtering,but alternatively may be deposited by MOCVD. Reverse axis piezoelectriclayers (e.g., reverse axis Aluminum Nitride (AlN) piezoelectric layers)may likewise be deposited via MOCVD. For the respective exampleresonators 400C, 400G shown in FIGS. 4C and 4G, the alternating axispiezoelectric stack 404C, 404G comprised of piezoelectric layers 405C,407C, 409C, 411C, 405G, 407G, 409G, 411G as well as interposer layers459C, 461C, 463C, 459G, 461G, 453G extending along stack thicknessdimension T27 fabricated using MOCVD on a silicon carbide substrate401C, 401G. For example, aluminum nitride of piezoelectric layers 405C,407C, 409C, 411C, 405G, 407G, 409G, 411G may grow nearly epitaxially onsilicon carbide (e.g., 4H SiC) by virtue of the small lattice mismatchbetween the polar axis aluminum nitride wurtzite structure and specificcrystal orientations of silicon carbide. Alternative small latticemismatch substrates may be used (e.g., sapphire, e.g., aluminum oxide).By varying the ratio of the aluminum and nitrogen in the depositionprecursors, an aluminum nitride film may be produced with the desiredpolarity (e.g., normal axis, e.g., reverse axis). For example, normalaxis aluminum nitride may be synthesized using MOCVD when a nitrogen toaluminum ratio in precursor gases approximately 1000. For example,reverse axis aluminum nitride may synthesized when the nitrogen toaluminum ratio is approximately 27000. In accordance with the foregoing,FIGS. 4C and 4G show MOCVD synthesized normal axis piezoelectric layer405C, 405G, MOCVD synthesized reverse axis piezoelectric layer 407C,407G, MOCVD synthesized normal axis piezoelectric layer 409C, 409G, andMOCVD synthesized reverse axis piezoelectric layer 411C, 411G. Forexample, normal axis piezoelectric layer 405C, 405G may be synthesizedby MOCVD in a deposition environment where the nitrogen to aluminum gasratio is relatively low, e.g., 1000 or less. Next an oxyaluminum nitridelayer, 459C at lower temperature, may be deposited by MOCVD that mayreverse axis (e.g., reverse axis polarity) of the growing aluminumnitride under MOCVD growth conditions, and has also been shown to beable to be deposited by itself under MOCVD growth conditions. Increasingthe nitrogen to aluminum ratio into the several thousands during theMOCVD synthesis may enable the reverse axis piezoelectric layer 407C,407G to be synthesized. Interposer layer 461C, 461G may be an oxidelayer such as, but not limited to, aluminum oxide or silicon dioxide.This oxide layer may be deposited in in a low temperature physical vapordeposition process such as sputtering or in a higher temperaturechemical vapor deposition process. Normal axis piezoelectric layer 409C,409G may be grown by MOCVD on top of interposer layer 461C, 461G usinggrowth conditions similar to the normal axis layer 405C, 405G, asdiscussed previously, namely MOCVD in a deposition environment where thenitrogen to aluminum gas ratio is relatively low, e.g., 1000 or less.Next an aluminum oxynitride, interposer layer 463C, 463G may bedeposited in a low temperature MOCVD process followed by a reverse axispiezoelectric layer 411C, 411G, synthesized in a high temperature MOCVDprocess and an atmosphere of nitrogen to aluminum ratio in the severalthousand range. Upon conclusion of these depositions, the piezoelectricstack 404C, 404G shown in FIGS. 4C and 4G may be realized.

FIG. 5 shows a schematic of an example ladder filter 500A (e.g.,millimeter wave ladder filter 500A, e.g., SHF ladder filter 500A, e.g.,EHF ladder filter 500A) using three series resonators of the bulkacoustic wave resonator structure of FIG. 1A (e.g., three bulk acousticmillimeter wave resonators, e.g., three bulk acoustic SHF waveresonators, e.g., three bulk acoustic EHF wave resonators), and two massloaded shunt resonators of the bulk acoustic wave resonator structure ofFIG. 1A (e.g., two mass loaded bulk acoustic millimeter wave resonators,e.g., two mass loaded bulk acoustic SHF wave resonators, e.g., two massloaded bulk acoustic EHF wave resonators), along with a simplified viewof the three series resonators. Accordingly, the example ladder filter500A (e.g., millimeter wave ladder filter 500A) is an electrical filter,comprising a plurality of bulk acoustic wave (BAW) resonators, e.g., ona substrate, in which the plurality of BAW resonators may comprise arespective first layer (e.g., bottom layer) of piezoelectric materialhaving a respective piezoelectrically excitable resonance mode. Theplurality of BAW resonators of the filter 500A may comprise a respectivetop acoustic reflector (e.g., top acoustic reflector electrode)including a respective initial top metal electrode layer and arespective first pair of top metal electrode layers electrically andacoustically coupled with the respective first layer (e.g., bottomlayer) of piezoelectric material to excite the respectivepiezoelectrically excitable resonance mode at a respective resonantfrequency. For example, the respective top acoustic reflector (e.g., topacoustic reflector electrode) may include the respective initial topmetal electrode layer and the respective first pair of top metalelectrode layers, and the foregoing may have a respective peak acousticreflectivity, e.g., in the millimeter wave band, e.g., in the Super HighFrequency (SHF) band, e.g., in the Extremely High Frequency (EHF) band,that includes the respective resonant frequency of the respective BAWresonator. The plurality of BAW resonators of the filter 500A maycomprise a respective bottom acoustic reflector (e.g., bottom acousticreflector electrode) including a respective initial bottom metalelectrode layer and a respective first pair of bottom metal electrodelayers electrically and acoustically coupled with the respective firstlayer (e.g., bottom layer) of piezoelectric material to excite therespective piezoelectrically excitable resonance mode at the respectiveresonant frequency. For example, the respective bottom acousticreflector (e.g., bottom acoustic reflector electrode) may include therespective initial bottom metal electrode layer and may include therespective first pair of bottom metal electrode layers, and theforegoing may have a respective peak acoustic reflectivity, e.g., in themillimeter wave band, e.g., in the Super High Frequency (SHF) band,e.g., in the Extremely High Frequency (EHF) band, that includes therespective resonant frequency of the respective BAW resonator. Therespective first layer (e.g., bottom layer) of piezoelectric materialmay be sandwiched between the respective top acoustic reflector an therespective bottom acoustic reflector. Further, the plurality of BAWresonators may comprise at least one respective additional layer ofpiezoelectric material, e.g., first middle piezoelectric layer. The atleast one additional layer of piezoelectric material may have thepiezoelectrically excitable main resonance mode with the respectivefirst layer (e.g., bottom layer) of piezoelectric material. Therespective first layer (e.g., bottom layer) of piezoelectric materialmay have a respective first piezoelectric axis orientation (e.g., normalaxis orientation) and the at least one respective additional layer ofpiezoelectric material may have a respective piezoelectric axisorientation (e.g., reverse axis orientation) that opposes the firstpiezoelectric axis orientation of the respective first layer ofpiezoelectric material. Further discussion of features that may beincluded in the plurality of BAW resonators of the filter 500A ispresent previously herein with respect to previous discussion of FIG. 1A

As shown in the schematic appearing at an upper section of FIG. 5 , theexample ladder filter 500A may include an input port comprising a firstnode 521A (InA), and may include a first series resonator 501A(Series1A) (e.g., first bulk acoustic millimeter wave resonator 501A)coupled between the first node 521A (InA) associated with the input portand a second node 522A. The example ladder filter 500A may also includea second series resonator 502A (Series2A) (e.g., second bulk acousticmillimeter wave resonator 502A) coupled between the second node 522A anda third node 523A. The example ladder filter 500A may also include athird series resonator 503A (Series3A) (e.g., third bulk acousticmillimeter wave resonator 503A) coupled between the third node 523A anda fourth node 524A (OutA), which may be associated with an output portof the ladder filter 500A. The example ladder filter 500A may alsoinclude a first mass loaded shunt resonator 511A (Shunt1A) (e.g., firstmass loaded bulk acoustic millimeter wave resonator 511A) coupledbetween the second node 522A and ground. The example ladder filter 500Amay also include a second mass loaded shunt resonator 512A (Shunt2A)(e.g., second mass loaded bulk acoustic millimeter wave resonator 512A)coupled between the third node 523 and ground.

Appearing at a lower section of FIG. 5 is the simplified view of thethree series resonators 501B (Series1B), 502B (Series2B), 503B(Series3B) in a serial electrically interconnected arrangement 500B, forexample, corresponding to series resonators 501A, 502A, 503A, of theexample ladder filter 500A. The three series resonators 501B (Series1B),502B (Series2B), 503B (Series3B), may be constructed as shown in thearrangement 500B and electrically interconnected in a way compatiblewith integrated circuit fabrication of the ladder filter. Although thefirst mass loaded shunt resonator 511A (Shunt1A) and the second massloaded shunt resonator 512A are not explicitly shown in the arrangement500B appearing at a lower section of FIG. 5 , it should be understoodthat the first mass loaded shunt resonator 511A (Shunt1A) and the secondmass loaded shunt resonator 512A are constructed similarly to what isshown for the series resonators in the lower section of FIG. 5 , butthat the first and second mass loaded shunt resonators 511A, 512A mayinclude mass layers, in addition to layers corresponding to those shownfor the series resonators in the lower section of FIG. 5 (e.g., thefirst and second mass loaded shunt resonators 511A, 512A may includerespective mass layers, in addition to respective top acousticreflectors of respective top metal electrode layers, may includerespective alternating axis stacks of piezoelectric material layers, andmay include respective bottom acoustic reflectors of bottom metalelectrode layers.) For example, all of the resonators of the ladderfilter may be co-fabricated using integrated circuit processes (e.g.,Complementary Metal Oxide Semiconductor (CMOS) compatible fabricationprocesses) on the same substrate (e.g., same silicon substrate). Theexample ladder filter 500A and serial electrically interconnectedarrangement 500B of series resonators 501A, 502A, 503A, may respectivelybe relatively small in size, and may respectively have a lateraldimension (X5) of less than approximately one millimeter.

For example, the serial electrically interconnected arrangement 500B ofthree series resonators 501B (Series1B), 502B (Series2B), 503B(Series3B), may include an input port comprising a first node 521B (InB)and may include a first series resonator 501B (Series1B) (e.g., firstbulk acoustic millimeter wave resonator 501B) coupled between the firstnode 521B (InB) associated with the input port and a second node 522B.The first node 521B (InB) may include bottom electrical interconnect569B electrically contacting a first bottom acoustic reflector of firstseries resonator 501B (Series1B) (e.g., first bottom acoustic reflectorelectrode of first series resonator 501B (Series1B). Accordingly, inaddition to including bottom electrical interconnect 569, the first node521B (InB) may also include the first bottom acoustic reflector of firstseries resonator 501B (Series1B) (e.g., first bottom acoustic reflectorelectrode of first series resonator 501B (Series1B)). The first bottomacoustic reflector of first series resonator 501B (Series1B) may includea stack of the plurality of bottom metal electrode layers 517 through525. The serial electrically interconnected arrangement 500B of threeseries resonators 501B (Series1B), 502B (Series2B), 503B (Series3B), mayinclude the second series resonator 502B (Series2B) (e.g., second bulkacoustic millimeter wave resonator 502B) coupled between the second node522B and a third node 523B. The third node 523B may include a secondbottom acoustic reflector of second series resonator 502B (Series2B)(e.g., second bottom acoustic reflector electrode of second seriesresonator 502B (Series2B)). The second bottom acoustic reflector ofsecond series resonator 502B (Series2B) (e.g., second bottom acousticreflector electrode of second series resonator 502B (Series2B)) mayinclude an additional stack of an additional plurality of bottom metalelectrode layers. The serial electrically interconnected arrangement500B of three series resonators 501B (Series1B), 502B (Series2B), 503B(Series3B), may also include the third series resonator 503B (Series3B)(e.g., third bulk acoustic millimeter wave resonator 503B) coupledbetween the third node 523B and a fourth node 524B (OutB). The thirdnode 523B, e.g., including the additional plurality of bottom metalelectrode layers, may electrically interconnect the second seriesresonator 502B (Series2B) and the third series resonator 503B(Series3B). The second bottom acoustic reflector (e.g., second bottomacoustic reflector electrode) of second series resonator 502B (Series2B)of the third node 523B, e.g., including the additional plurality ofbottom metal electrode layers, may be a mutual bottom acoustic reflector(e.g., mutual bottom acoustic reflector electrode), and may likewiseserve as bottom acoustic reflector (e.g., bottom acoustic reflectorelectrode) of third series resonator 503B (Series3B). The fourth node524B (OutB) may be associated with an output port of the serialelectrically interconnected arrangement 500B of three series resonators501B (Series1B), 502B (Series2B), 503B (Series3B). The fourth node 524B(OutB) may include electrical interconnect 571C.

The stack of the plurality of bottom metal electrode layers 517 through525 are associated with the first bottom acoustic reflector (e.g., firstbottom acoustic reflector electrode) of first series resonator 501B(Series1B). The additional stack of the additional plurality of bottommetal electrode layers (e.g., of the third node 523B) may be associatedwith the mutual bottom acoustic reflector (e.g., mutual bottom acousticreflector electrode) of both the second series resonant 502B (Series2B)and the third series resonator 503B (Series3B). Although stacks ofrespective five bottom metal electrode layers are shown in simplifiedview in FIG. 5 , it should be understood that the stacks may includerespective larger numbers of bottom metal electrode layers, e.g.,respective nine top metal electrode layers. Further, the first seriesresonator (Series1B), and the second series resonant 502B (Series2B) andthe third series resonator 503B (Series3B) may all have the same, orapproximately the same, or different (e.g., achieved by means ofadditional mass loading layers) resonant frequency (e.g., the same, orapproximately the same, or different main resonant frequency). Forexample, small additional massloads (e.g., a tenth of the main shuntmass-load) of series and shunt resonators may help to reduce pass-bandripples in insertion loss, as may be appreciated by one with skill inthe art. The bottom metal electrode layers 517 through 525 and theadditional plurality of bottom metal electrode layers (e.g., of themutual bottom acoustic reflector, e.g., of the third node 523B) may haverespective thicknesses that are related to wavelength (e.g., acousticwavelength) for the resonant frequency (e.g., main resonant frequency)of the series resonators (e.g., first series resonator 501B (Series1B),e.g., second series resonator 502B, e.g., third series resonator(503B)). Various embodiments for series resonators (e.g., first seriesresonator 501B (Series1B), e.g., second series resonator 502B, e.g.,third series resonator (503B)) having various relatively higher resonantfrequency (e.g., higher main resonant frequency) may have relativelythinner bottom metal electrode thicknesses, e.g., scaled thinner withrelatively higher resonant frequency (e.g., higher main resonantfrequency). Similarly, various embodiments of the series resonators(e.g., first series resonator 501B (Series1B), e.g., second seriesresonator 502B, e.g., third series resonator (503B)) having variousrelatively lower resonant frequency (e.g., lower main resonantfrequency) may have relatively thicker bottom metal electrode layerthicknesses, e.g., scaled thicker with relatively lower resonantfrequency (e.g., lower main resonant frequency). The bottom metalelectrode layers 517 through 525 and the additional plurality of bottommetal electrode layers (e.g., of the mutual bottom acoustic reflector,e.g., of the third node 523B) may include members of pairs of bottommetal electrodes having respective thicknesses of one quarter wavelength(e.g., one quarter acoustic wavelength) at the resonant frequency (e.g.,main resonant frequency) of the series resonators (e.g., first seriesresonator 501B (Series1B), e.g., second series resonator 502B, e.g.,third series resonator (503B)). The stack of bottom metal electrodelayers 517 through 525 and the stack of additional plurality of bottommetal electrode layers (e.g., of the mutual bottom acoustic reflector,e.g., of the third node 523B) may include respective alternating stacksof different metals, e.g., different metals having different acousticimpedances (e.g., alternating relatively high acoustic impedance metalswith relatively low acoustic impedance metals). The foregoing mayprovide acoustic impedance mismatches for facilitating acousticreflectivity (e.g., millimeter acoustic wave reflectivity) of the firstbottom acoustic reflector (e.g., first bottom acoustic reflectorelectrode) of the first series resonator 501B (Series1B) and the mutualbottom acoustic reflector (e.g., of the third node 523B) of the secondseries resonator 502B (Series2B) and the third series resonator 503B(Series3B).

A first top acoustic reflector (e.g., first top acoustic reflectorelectrode) may comprise a first stack of a first plurality of top metalelectrode layers 535C through 543C of the first series resonator 501B(Series1B). A second top acoustic reflector (e.g., second top acousticreflector electrode) may comprise a second stack of a second pluralityof top metal electrode layers 535D through 543D of the second seriesresonator 502B (Series2B). A third top acoustic reflector (e.g., thirdtop acoustic reflector electrode) may comprise a third stack of a thirdplurality of top metal electrode layers 535E through 543E of the thirdseries resonator 503B (Series3B). Although stacks of respective five topmetal electrode layers are shown in simplified view in FIG. 5 , inshould be understood that the stacks may include respective largernumbers of top metal electrode layers, e.g., respective nine bottommetal electrode layers. Further, the first plurality of top metalelectrode layers 535C through 543C, the second plurality of top metalelectrode layers 535D through 543D, and the third plurality of top metalelectrode layers 535E through 543E may have respective thicknesses thatare related to wavelength (e.g., acoustic wavelength) for the resonantfrequency (e.g., main resonant frequency) of the series resonators(e.g., first series resonator 501B (Series1B), e.g., second seriesresonator 502B, e.g., third series resonator (503B)). Variousembodiments for series resonators (e.g., first series resonator 501B(Series1B), e.g., second series resonator 502B, e.g., third seriesresonator (503B)) having various relatively higher resonant frequency(e.g., higher main resonant frequency) may have relatively thinner topmetal electrode thicknesses, e.g., scaled thinner with relatively higherresonant frequency (e.g., higher main resonant frequency). Similarly,various embodiments of the series resonators (e.g., first seriesresonator 501B (Series1B), e.g., second series resonator 502B, e.g.,third series resonator (503B)) having various relatively lower resonantfrequency (e.g., lower main resonant frequency) may have relativelythicker top metal electrode layer thicknesses, e.g., scaled thicker withrelatively lower resonant frequency (e.g., lower main resonantfrequency). The first plurality of top metal electrode layers 535Cthrough 543C, the second plurality of top metal electrode layers 535Dthrough 543D, and the third plurality of top metal electrode layers 535Ethrough 543E may include members of pairs of bottom metal electrodeshaving respective thicknesses of one quarter wavelength (e.g., onequarter acoustic wavelength) of the resonant frequency (e.g., mainresonant frequency) of the series resonators (e.g., first seriesresonator 501B (Series1B), e.g., second series resonator 502B, e.g.,third series resonator (503B)). The first stack of the first pluralityof top metal electrode layers 535C through 543C, the second stack of thesecond plurality of top metal electrode layers 535D through 543D, andthe third stack of the third plurality of top metal electrode layers535E through 543E may include respective alternating stacks of differentmetals, e.g., different metals having different acoustic impedances(e.g., alternating relatively high acoustic impedance metals withrelatively low acoustic impedance metals). The foregoing may provideacoustic impedance mismatches for facilitating acoustic reflectivity(e.g., millimeter acoustic wave reflectivity) of the top acousticreflectors (e.g., the first top acoustic reflector of the first seriesresonator 501B (Series1B), e.g., the second top acoustic reflector ofthe second series resonator 502B (Series2B), e.g., the third topacoustic reflector of the third series resonator 503B (Series3B)).Although not explicitly shown in the FIG. 5 simplified views of metalelectrode layers of the series resonators, respective pluralities oflateral features (e.g., respective pluralities of step features) may besandwiched between metal electrode layers (e.g., between respectivepairs of top metal electrode layers, e.g., between respective firstpairs of top metal electrode layers 537C, 539C, 537D, 539D, 537E, 539E,and respective second pairs of top metal electrode layers 541C, 543C,541D, 543D, 541E, 543E. The respective pluralities of lateral featuresmay, but need not, limit parasitic lateral acoustic modes (e.g.,facilitate suppression of spurious modes) of the bulk acoustic waveresonators of FIG. 5 (e.g., of the series resonators, the mass loadedseries resonators, and the mass loaded shunt resonators).

The first series resonator 501B (Series1B) may comprise a firstalternating axis stack, e.g., an example first stack of four layers ofalternating axis piezoelectric material, 505C through 511C. The secondseries resonator 502B (Series2B) may comprise a second alternating axisstack, e.g., an example second stack of four layers of alternating axispiezoelectric material, 505D through 511D. The third series resonator503B (Series3B) may comprise a third alternating axis stack, e.g., anexample third stack of four layers of alternating axis piezoelectricmaterial, 505E through 511E. The first, second and third alternatingaxis piezoelectric stacks may comprise layers of Aluminum Nitride (AlN)having alternating C-axis wurtzite structures. For example,piezoelectric layers 505C, 505D, 505E, 509C, 509D, 509E have normal axisorientation. For example, piezoelectric layers 507C, 507D, 507E, 511C,511D, 511E have reverse axis orientation. Members of the first stack offour layers of alternating axis piezoelectric material, 505C through511C, and members of the second stack of four layers of alternating axispiezoelectric material, 505D through 511D, and members of the thirdstack of four layers of alternating axis piezoelectric material, 505Ethrough 511E, may have respective thicknesses that are related towavelength (e.g., acoustic wavelength) for the resonant frequency (e.g.,main resonant frequency) of the series resonators (e.g., first seriesresonator 501B (Series1B), e.g., second series resonator 502B, e.g.,third series resonator (503B)). Various embodiments for seriesresonators (e.g., first series resonator 501B (Series1B), e.g., secondseries resonator 502B, e.g., third series resonator (503B)) havingvarious relatively higher resonant frequency (e.g., higher main resonantfrequency) may have relatively thinner piezoelectric layer thicknesses,e.g., scaled thinner with relatively higher resonant frequency (e.g.,higher main resonant frequency). Similarly, various embodiments of theseries resonators (e.g., first series resonator 501B (Series1B), e.g.,second series resonator 502B, e.g., third series resonator (503B))having various relatively lower resonant frequency (e.g., lower mainresonant frequency) may have relatively thicker piezoelectric layerthicknesses, e.g., scaled thicker with relatively lower resonantfrequency (e.g., lower main resonant frequency). The example first stackof four layers of alternating axis piezoelectric material, 505C through511C, the example second stack of four layers of alternating axispiezoelectric material, 505D through 511D and the example third stack offour layers of alternating axis piezoelectric material, 505D through511D may include stack members of piezoelectric layers having respectivethicknesses of approximately one half wavelength (e.g., one halfacoustic wavelength) at the resonant frequency (e.g., main resonantfrequency) of the series resonators (e.g., first series resonator 501B(Series1B), e.g., second series resonator 502B, e.g., third seriesresonator (503B)).

The example first stack of four layers of alternating axis piezoelectricmaterial, 505C through 511C, may include a first three members ofinterposer layers 559C, 561C, 563C respectively sandwiched between thecorresponding four layers of alternating axis piezoelectric material,505C through 511C. The example second stack of four layers ofalternating axis piezoelectric material, 505D through 511D, may includea second three members of interposer layers 559D, 561D, 563Drespectively sandwiched between the corresponding four layers ofalternating axis piezoelectric material, 505D through 511D. The examplethird stack of four layers of alternating axis piezoelectric material,505E through 511E, may include a third three members of interposerlayers 559E, 561E, 563E respectively sandwiched between thecorresponding four layers of alternating axis piezoelectric material,505E through 511E. One or more (e.g., one or a plurality of) interposerlayers may be metal interposer layers. The metal interposer layers maybe relatively high acoustic impedance metal interposer layers (e.g.,using relatively high acoustic impedance metals such as Tungsten (W) orMolybdenum (Mo)). Such metal interposer layers may (but need not)flatten stress distribution across adjacent piezoelectric layers, andmay (but need not) raise effective electromechanical couplingcoefficient (Kt2) of adjacent piezoelectric layers. Alternatively oradditionally, one or more (e.g., one or a plurality of) interposerlayers may be dielectric interposer layers. The dielectric of thedielectric interposer layers may be a dielectric that has a positiveacoustic velocity temperature coefficient, so acoustic velocityincreases with increasing temperature of the dielectric. The dielectricof the dielectric interposer layers may be, for example, silicondioxide. Dielectric interposer layers may, but need not, facilitatecompensating for frequency response shifts with increasing temperature.Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may comprise metal and dielectric for respectiveinterposer layers. Alternatively or additionally, one or more (e.g., oneor a plurality of) interposer layers may be formed of different metallayers. Alternatively or additionally, one or more (e.g., one or aplurality of) interposer layers may be formed of different dielectriclayers. The first series resonator 501B (Series1B), the second seriesresonator 502B (Series2B) and the third series resonator 503B (Series3B)may have respective etched edge regions 553C, 553D, 553E, and respectivelaterally opposing etched edge regions 554C, 554D, 554E. Reference ismade to resonator mesa structures as have already been discussed indetail previously herein. Accordingly, they are not discussed again indetail at this point. Briefly, respective first, second and third mesastructures of the respective first series resonator 501B (Series1B), therespective second series resonator 502B (Series2B) and the respectivethird series resonator 503B (Series3B) may extend between respectiveetched edge regions 553C, 553D, 553E, and respective laterally opposingetched edge regions 554C, 554D, 554E of the respective first seriesresonator 501B (Series1B), the respective second series resonator 502B(Series2B) and the respective third series resonator 503B (Series3B).The second bottom acoustic reflector of second series resonator 502B(Series2B) of the third node 523B, e.g., including the additionalplurality of bottom metal electrode layers may be a second mesastructure. For example, this may be a mutual second mesa structurebottom acoustic reflector 523B, and may likewise serve as bottomacoustic reflector of third series resonator 503B (Series3B).Accordingly, this mutual second mesa structure bottom acoustic reflector523B may extend between etched edge region 553E of the third seriesresonator 503B (Series3B) and the laterally opposing etched edge region554D of the third series resonator 503B (Series3B).

FIG. 6 shows a schematic of an example ladder filter 600A (e.g.,millimeter wave ladder filter 600A, e.g., SHF wave ladder filter 600A,e.g., EHF wave ladder filter 600A) using five series resonators of thebulk acoustic wave resonator structure of FIG. 1A (e.g., five bulkacoustic millimeter wave resonators), and four mass loaded shuntresonators of the bulk acoustic wave resonator structure of FIG. 1A(e.g., four mass loaded bulk acoustic millimeter wave resonators), alongwith a simplified top view of the nine resonators interconnected in theexample ladder filter 600B, and lateral dimensions of the example ladderfilter 600B. As shown in the schematic appearing at an upper section ofFIG. 6 , the example ladder filter 600A may include an input portcomprising a first node 621A (InputA E1TopA), and may include a firstseries resonator 601A (Ser1A) (e.g., first bulk acoustic millimeter waveresonator 601A) coupled between the first node 621A (InputA E1TopA)associated with the input port and a second node 622A (E1BottomA). Theexample ladder filter 600A may also include a second series resonator602A (Ser2A) (e.g., second bulk acoustic millimeter wave resonator 602A)coupled between the second node 622A (E1BottomA) and a third node 623A(E3TopA). The example ladder filter 600A may also include a third seriesresonator 603A (Ser3A) (e.g., third bulk acoustic millimeter waveresonator 603A) coupled between the third node 623A (E3TopA) and afourth node 624A (E2BottomA). The example ladder filter 600A may alsoinclude a fourth series resonator 604A (Ser4A) (e.g., fourth bulkacoustic millimeter wave resonator 604A) coupled between the fourth node624A (E2BottomA) and a fifth node 625A (E4TopA). The example ladderfilter 600A may also include a fifth series resonator 605A (Ser5A)(e.g., fifth bulk acoustic millimeter wave resonator 605A) coupledbetween the fifth node 625A (E4TopA) and a sixth node 626A (OutputAE4BottomA), which may be associated with an output port of the ladderfilter 600A. The example ladder filter 600A may also include a firstmass loaded shunt resonator 611A (Sh1A) (e.g., first mass loaded bulkacoustic millimeter wave resonator 611A) coupled between the second node622A (E1BottomA) and a first grounding node 631A (E2TopA). The exampleladder filter 600A may also include a second mass loaded shunt resonator612A (Sh2A) (e.g., second mass loaded bulk acoustic millimeter waveresonator 612A) coupled between the third node 623A (E3TopA) and asecond grounding node 632A (E3BottomA). The example ladder filter 600Amay also include a third mass loaded shunt resonator 613A (Sh3A) (e.g.,third mass loaded bulk acoustic millimeter wave resonator 613A) coupledbetween the fourth node 624A (E2BottomA) and the first grounding node631A (E2TopA). The example ladder filter 600A may also include a fourthmass loaded shunt resonator 614A (Sh4A) (e.g., fourth mass loaded bulkacoustic millimeter wave resonator 614A) coupled between the fifth node625A (E4TopA) and the second grounding node 632A (E3BottomA). The firstgrounding node 631A (E2TopA) and the second grounding node 632A(E3BottomA) may be interconnected to each other, and may be connected toground, through an additional grounding connection(AdditionalConnection).

Appearing at a lower section of FIG. 6 is the simplified top view of thenine resonators interconnected in the example ladder filter 600B, andlateral dimensions of the example ladder filter 600B. The example ladderfilter 600B may include an input port comprising a first node 621B(InputA E1TopB), and may include a first series resonator 601B (Ser1B)(e.g., first bulk acoustic millimeter wave resonator 601B) coupledbetween (e.g., sandwiched between) the first node 621B (InputA E1TopB)associated with the input port and a second node 622B (E1BottomB). Theexample ladder filter 600B may also include a second series resonator602B (Ser2B) (e.g., second bulk acoustic millimeter wave resonator 602B)coupled between (e.g., sandwiched between) the second node 622B(E1BottomB) and a third node 623B (E3TopB). The example ladder filter600B may also include a third series resonator 603B (Ser3B) (e.g., thirdbulk acoustic millimeter wave resonator 603B) coupled between (e.g.,sandwiched between) the third node 623B (E3TopB) and a fourth node 624B(E2BottomB). The example ladder filter 600B may also include a fourthseries resonator 604B (Ser4B) (e.g., fourth bulk acoustic millimeterwave resonator 604B) coupled between (e.g., sandwiched between) thefourth node 624B (E2BottomB) and a fifth node 625B (E4TopB). The exampleladder filter 600B may also include a fifth series resonator 605B(Ser5B) (e.g., fifth bulk acoustic millimeter wave resonator 605B)coupled between (e.g., sandwiched between) the fifth node 625B (E4TopB)and a sixth node 626B (OutputB E4BottomB), which may be associated withan output port of the ladder filter 600B. The example ladder filter 600Bmay also include a first mass loaded shunt resonator 611B (Sh1B) (e.g.,first mass loaded bulk acoustic millimeter wave resonator 611B) coupledbetween (e.g., sandwiched between) the second node 622B (E1BottomB) anda first grounding node 631B (E2TopB). The example ladder filter 600B mayalso include a second mass loaded shunt resonator 612B (Sh2B) (e.g.,second mass loaded bulk acoustic millimeter wave resonator 612B) coupledbetween (e.g., sandwiched between) the third node 623B (E3TopB) and asecond grounding node 632B (E3BottomB). The example ladder filter 600Bmay also include a third mass loaded shunt resonator 613B (Sh3B) (e.g.,third mass loaded bulk acoustic millimeter wave resonator 613B) coupledbetween (e.g., sandwiched between) the fourth node 624B (E2BottomB) andthe first grounding node 631B (E2TopB). The example ladder filter 600Bmay also include a fourth mass loaded shunt resonator 614B (Sh4B) (e.g.,fourth mass loaded bulk acoustic millimeter wave resonator 614B) coupledbetween (e.g., sandwiched between) the fifth node 625B (E4TopB) and thesecond grounding node 632B (E3BottomB). The first grounding node 631B(E2TopB) and the second grounding node 632B (E3BottomB) may beinterconnected to each other, and may be connected to ground, through anadditional grounding connection, not shown in the lower section of FIG.6 . The example ladder filter 600B may respectively be relatively smallin size, and may respectively have lateral dimensions (X6 by Y6) of lessthan approximately one millimeter by one millimeter.

FIG. 7 shows an schematic of example inductors modifying an examplelattice filter 700 using a first pair of series resonators 701A (Se1T),702A (Se2T), (e.g., two bulk acoustic millimeter wave resonators) of thebulk acoustic wave resonator structure of FIG. 1A, a second pair ofseries resonators 701B (Se2B), 702B (Se2B), (e.g., two additional bulkacoustic millimeter wave resonators) of the bulk acoustic wave resonatorstructure of FIG. 1A and two pairs of cross coupled mass loaded shuntresonators 701C (Sh1C), 702D (Sh2C), 703C (Sh3C), 704C (Sh4C), (e.g.,four mass loaded bulk acoustic millimeter wave resonators) of the bulkacoustic wave resonator structure of FIG. 1A. As shown in the schematicof FIG. 7 , the example inductor modified lattice filter 700 may includea first top series resonator 701A (Se1T) (e.g., first top bulk acousticmillimeter wave resonator 701A) coupled between a first top node 721Aand a second top node 722A. The example inductor modified lattice filter700 may also include a second top series resonator 702A (Se2T) (e.g.,second top bulk acoustic millimeter wave resonator 702A) coupled betweenthe second top node 722A and a third top node 723A.

The example inductor modified lattice filter 700 may include a firstbottom series resonator 701B (Se1B) (e.g., first bottom bulk acousticmillimeter wave resonator 701B) coupled between a first bottom node 721Band a second bottom node 722B. The example inductor modified latticefilter 700 may also include a second bottom series resonator 702B (Se2B)(e.g., second bottom bulk acoustic millimeter wave resonator 702B)coupled between the second bottom node 722B and a third bottom node723B. The example inductor modified lattice filter 700 may include afirst cross-coupled mass loaded shunt resonator 701C (Sh1C) (e.g., firstmass loaded bulk acoustic millimeter wave resonator 701C) coupledbetween the first top node 721A and the second bottom node 722B. Theexample inductor modified lattice filter 700 may also include a secondcross-coupled mass loaded shunt resonator 702C (Sh2C) (e.g., second massloaded bulk acoustic millimeter wave resonator 702C) coupled between thesecond top node 722A and the first bottom node 721B. The exampleinductor modified lattice filter 700 may include a third cross-coupledmass loaded shunt resonator 703C (Sh3C) (e.g., third mass loaded bulkacoustic millimeter wave resonator 703C) coupled between the second topnode 722A and the third bottom node 723B. The example inductor modifiedlattice filter 700 may also include a fourth cross-coupled mass loadedshunt resonator 704C (Sh4C) (e.g., fourth mass loaded bulk acousticmillimeter wave resonator 704C) coupled between the third top node 723Aand the second bottom node 722B. The example inductor modified latticefilter 700 may include a first inductor 711 (L1) coupled between thefirst top node 721A and the first bottom node 721B. The example inductormodified lattice filter 700 may include a second inductor 712 (L2)coupled between the second top node 722A and the second bottom node722B. The example inductor modified lattice filter 700 may include athird inductor 713 (L3) coupled between the third top node 723A and thethird bottom node 723B.

FIGS. 8A and 8B show an example oscillator 800A, 800B (e.g., millimeterwave oscillator 800A, 800B, e.g., Super High Frequency (SHF) waveoscillator 800A, 800B, e.g., Extremely High Frequency (EHF) waveoscillator 800A, 800B) using the bulk acoustic wave resonator structureof FIG. 1A. For example, FIGS. 8A and 8B shows simplified views of bulkacoustic wave resonator 801A, 801B electrically coupled with electricaloscillator circuitry (e.g., active oscillator circuitry 802A, 802B)through phase compensation circuitry 803A, 803B (Φcomp). The exampleoscillator 800A, 800B may be a negative resistance oscillator, e.g., inaccordance with a one-port model as shown in FIGS. 8A and 8B. Theelectrical oscillator circuitry, e.g., active oscillator circuitry, mayinclude one or more suitable active devices (e.g., one or more suitablyconfigured amplifying transistors) to generate a negative resistancecommensurate with resistance of the bulk acoustic wave resonator 801A,801B. In other words, energy lost in bulk acoustic wave resonator 801A,801B may be replenished by the active oscillator circuitry, thusallowing steady oscillation, e.g., steady millimeter wave oscillation.To ensure oscillation start-up, active gain (e.g., negative resistance)of active oscillator circuitry 802A, 802B may be greater than one. Asillustrated on opposing sides of a notional dashed line in FIGS. 8A and8B, the active oscillator circuitry 802A, 802B may have a complexreflection coefficient of the active oscillator circuitry (Γamp), andthe bulk acoustic wave resonator 801A, 801B together with the phasecompensation circuitry 803A, 803B (Φcomp) may have a complex reflectioncoefficient (Γres). To provide for the steady oscillation, e.g., steadymillimeter wave oscillation, a magnitude may be greater than one for|Γamp Γres|, e.g., magnitude of a product of the complex reflectioncoefficient of the active oscillator circuitry (Γamp) and the complexreflection coefficient (Γres) of the resonator to bulk acoustic waveresonator 801A, 801B together with the phase compensation circuitry803A, 803B (Φcomp) may be greater than one. Further, to provide for thesteady oscillation, e.g., steady millimeter wave oscillation, phaseangle may be an integer multiple of three-hundred-sixty degrees for∠Γamp Γres, e.g., a phase angle of the product of the complex reflectioncoefficient of the active oscillator circuitry (Γamp) and the complexreflection coefficient (Γres) of the resonator to bulk acoustic waveresonator 801A, 801B together with the phase compensation circuitry803A, 803B (Φcomp) may be an integer multiple of three-hundred-sixtydegrees. The foregoing may be facilitated by phase selection, e.g.,electrical length selection, of the phase compensation circuitry 803A,803B (Φcomp).

In the simplified view of FIG. 8A, the bulk acoustic wave resonator 801A(e.g., bulk acoustic millimeter wave resonator) includes first normalaxis piezoelectric layer 805A, first reverse axis piezoelectric layer807A, and another normal axis piezoelectric layer 809A, and anotherreverse axis piezoelectric layer 811A arranged in a four piezoelectriclayer alternating axis stack arrangement sandwiched between multilayermetal acoustic millimeter wave reflector top electrode 815A andmultilayer metal acoustic millimeter wave reflector bottom electrode813A.

General structures and applicable teaching of this disclosure for themultilayer metal acoustic millimeter wave reflector top electrode 815Aand the multilayer metal acoustic millimeter wave reflector bottomelectrode 813A have already been discussed in detail previously hereinwith respect of FIGS. 1A and 4A through 4G, which for brevity areincorporated by reference rather than repeated fully here. As alreadydiscussed, these structures are directed to respective pairs of metalelectrode layers, in which a first member of the pair has a relativelylow acoustic impedance (relative to acoustic impedance of an othermember of the pair), in which the other member of the pair has arelatively high acoustic impedance (relative to acoustic impedance ofthe first member of the pair), and in which the respective pairs ofmetal electrode layers have layer thicknesses corresponding to onequarter wavelength (e.g., one quarter acoustic wavelength) at a mainresonant frequency of the resonator. Accordingly, it should beunderstood that the bulk acoustic millimeter wave resonator 801A shownin FIG. 8A includes multilayer metal acoustic millimeter wave reflectortop electrode 815A and multilayer metal acoustic millimeter wavereflector bottom electrode 815B in which the respective pairs of metalelectrode layers may include layer thicknesses corresponding to aquarter wavelength (e.g., one quarter of an acoustic wavelength) at amillimeter band main resonant frequency of the respective bulk acousticmillimeter wave resonator 801A. The multilayer metal acoustic millimeterwave reflector top electrode 815A may include an initial top metalelectrode layer and a first pair of top metal electrode layerselectrically and acoustically coupled with the four piezoelectric layeralternating axis stack arrangement (e.g., with the first normal axispiezoelectric layer 805A, e.g., with first reverse axis piezoelectriclayer 807A, e.g., with another normal axis piezoelectric layer 809A,e.g., with another reverse axis piezoelectric layer 811A) to excite thepiezoelectrically excitable resonance mode at the resonant frequency.For example, the multilayer metal acoustic millimeter wave reflector topelectrode 815A may include the initial top metal electrode layer and therespective first pair of top metal electrode layers, and the foregoingmay have a respective peak acoustic reflectivity at a frequency in themillimeter wave band that includes the respective resonant frequency ofthe respective BAW resonator. Similarly, the multilayer metal acousticmillimeter wave reflector bottom electrode 813A may include an initialbottom metal electrode layer and a first pair of bottom metal electrodelayers electrically and acoustically coupled with the four piezoelectriclayer alternating axis stack arrangement (e.g., with the first normalaxis piezoelectric layer 805A, e.g., with first reverse axispiezoelectric layer 807A, e.g., with another normal axis piezoelectriclayer 809A, e.g., with another reverse axis piezoelectric layer 811A) toexcite the piezoelectrically excitable resonance mode at the resonantfrequency. For example, the multilayer metal acoustic millimeter wavereflector bottom electrode 813A may include the initial bottom metalelectrode layer and the respective first pair of bottom metal electrodelayers, and the foregoing may have a respective peak acousticreflectivity at a frequency in the millimeter wave band that includesthe respective resonant frequency of the respective BAW resonator.

An output 816A of the oscillator 800A may be coupled to the bulkacoustic wave resonator 801A (e.g., coupled to multilayer metal acousticmillimeter wave reflector top electrode 815A) It should be understoodthat interposer layers as discussed previously herein with respect toFIG. 1A are explicitly shown in the simplified view the exampleresonator 801A shown in FIG. 8A. Such interposer layers may be includedand interposed between adjacent piezoelectric layers. For example, afirst interposer layer is arranged between first normal axispiezoelectric layer 805A and first reverse axis piezoelectric layer807A. For example, a second interposer layer is arranged between firstreverse axis piezoelectric layer 807A and another normal axispiezoelectric layer 809A. For example, a third interposer is arrangedbetween another normal axis piezoelectric layer 809A and another reverseaxis piezoelectric layer 807A. As discussed previously herein, suchinterposer may be metal or dielectric, and may, but need not providevarious benefits, as discussed previously herein. Alternatively oradditionally, interposer layers may comprise metal and dielectric.Alternatively or additionally, one or more (e.g., one or a plurality of)interposer layers may be formed of different metal layers. Alternativelyor additionally, one or more (e.g., one or a plurality of) interposerlayers may be formed of different dielectric layers.

A notional heavy dashed line is used in depicting an etched edge region853A associated with example resonator 801A. The example resonator 801Amay also include a laterally opposing etched edge region 854A arrangedopposite from the etched edge region 853A. The etched edge region 853A(and the laterally opposing etch edge region 854A) may similarly extendthrough various members of the example resonator 801A of FIG. 8A, in asimilar fashion as discussed previously herein with respect to theetched edge region 253D (and the laterally opposing etch edge region254D) of example resonator 2001D shown in FIG. 2B. As shown in FIG. 8A,a first mesa structure corresponding to the stack of four piezoelectricmaterial layers 805A, 807A, 809A, 811A may extend laterally between(e.g., may be formed between) etched edge region 853A and laterallyopposing etched edge region 854A. A second mesa structure correspondingto multilayer metal acoustic millimeter wave reflector bottom electrode813A may extend laterally between (e.g., may be formed between) etchededge region 853A and laterally opposing etched edge region 854A. Thirdmesa structure corresponding to multilayer metal acoustic millimeterwave reflector top electrode 815A may extend laterally between (e.g.,may be formed between) etched edge region 853A and laterally opposingetched edge region 854A. Although not explicitly shown in the FIG. 8Asimplified view of metal electrode layers, e.g., multilayer metalacoustic millimeter wave reflector top electrode 815A, a plurality oflateral features (e.g., plurality of step features) may be sandwichedbetween metal electrode layers (e.g., between pairs of top metalelectrode layers. The plurality of lateral features may, but need not,limit parasitic lateral acoustic modes of the example bulk acoustic waveresonator of FIG. 8A.

FIG. 8B shows a schematic of and example circuit implementation of theoscillator shown in FIG. 8A. Active oscillator circuitry 802B mayinclude active elements, symbolically illustrated in FIG. 8B byalternating voltage source 804B (Vs) coupled through negative resistance806B (Rneg), e.g., active gain element 806B, to example bulk acousticwave resonator 801B (e.g., bulk acoustic millimeter wave resonator) viaphase compensation circuitry 803B (Φcomp). The representation of examplebulk acoustic wave resonator 801B (e.g., bulk acoustic millimeter waveresonator) may include passive elements, symbolically illustrated inFIG. 8B by electrode ohmic loss parasitic series resistance 808B (Rs),motional capacitance 810B (Cm), acoustic loss motional resistance 812B(Rm), motional inductance 814B (Lm), static or plate capacitance 816B(Co), and acoustic loss parasitic 818B (Ro). An output 816B of theoscillator 800B may be coupled to the bulk acoustic wave resonator 801B(e.g., coupled to a multilayer metal acoustic millimeter wave reflectortop electrode of bulk acoustic wave resonator 801B).

FIGS. 9A and 9B are simplified diagrams of a frequency spectrumillustrating application frequencies and application frequency bands ofthe example bulk acoustic wave resonators shown in FIG. 1A and FIGS. 4Athrough 4G, and the example filters shown in FIGS. 5 through 7 , and theexample oscillators shown in FIGS. 8A and 8B. A widely used standard todesignate frequency bands in the microwave range by letters isestablished by the United States Institute of Electrical and ElectronicEngineers (IEEE). In accordance with standards published by the IEEE, asdefined herein, and as shown in FIGS. 9A and 9B are application bands asfollows: S Band (2 GHz-4 GHz), C Band (4 GHz-8 GHz), X Band (8 GHz-12GHz), Ku Band (12 GHz-18 GHz), K Band (18 GHz-27 GHz), Ka Band (27GHz-40 GHz), V Band (40 GHz-75 GHz), and W Band (75 GHz-110 GHz). FIG.9A shows a first frequency spectrum portion 9000A in a range from threeGigahertz (3 GHz) to eight Gigahertz (8 GHz), including applicationbands of S Band (2 GHz-4 GHz) and C Band (4 GHz-8 GHz). As describedsubsequently herein, the 3rd Generation Partnership Project standardsorganization (e.g., 3GPP) has standardized various 5G frequency bands.For example, included is a first application band 9010 (e.g., 3GPP 5Gn77 band) (3.3 GHz-4.2 GHz) configured for fifth generation broadbandcellular network (5G) applications. As described subsequently herein,the first application band 9010 (e.g., 5G n77 band) includes a 5Gsub-band 9011 (3.3 GHz-3.8 GHz). The 3GPP 5G sub-band 9011 includes LongTerm Evolution broadband cellular network (LTE) application sub-bands9012 (3.4 GHz-3.6 GHz), 9013 (3.6 GHz-3.8 GHz), and 9014 (3.55 GHz-3.7GHz). A second application band 9020 (4.4 GHz-5.0 GHz) includes asub-band 9021 for China specific applications. Discussed next areUnlicensed National Information Infrastructure (UNII) bands. A thirdapplication band 9030 includes a UNII-1 band 9031 (5.15 GHz-5.25 GHz)and a UNII-2A band 9032 (5.25 GHz 5.33 GHz). An LTE band 9033 (LTE Band252) overlaps the same frequency range as the UNII-1 band 6031. A fourthapplication band 9040 includes a UNII-2C band 9041 (5.490 GHz-5.735GHz), a UNII-3 band 9042 (5.735 GHz-5.85 GHz), a UNII-4 band 9043 (5.85GHz-5.925 GHz), a UNII-5 band 9044 (5.925 GHz-6.425 GHz), a UNII-6 band9045 (6.425 GHz-6.525 GHz), a UNII-7 band 9046 (6.525 Ghz-6.875 Ghz),and a UNII-8 band 9047 (6.875 GHz-7125 Ghz). An LTE band 9048 overlapsthe same frequency range (5.490 GHz-5.735 GHz) as the UNII-3 band 9042.A sub-band 9049A shares the same frequency range as the UNII-4 band9043. An LTE band 9049B shares a subsection of the same frequency range(5.855 GHz-5.925 GHz).

FIG. 9B shows a second frequency spectrum portion 9000B in a range fromeight Gigahertz (8 GHz) to one-hundred and ten Gigahertz (110 GHz),including application bands of X Band (8 Ghz-12 Ghz), Ku Band (12 Ghz-18Ghz), K Band (18 Ghz-27 Ghz), Ka Band (27 Ghz-40 Ghz), V Band (40 Ghz-75Ghz), and W Band (75 Ghz-110 Ghz). A fifth application band 9050includes 3GPP 5G bands configured for fifth generation broadbandcellular network (5G) applications, e.g., 3GPP 5G n258 band 9051 (24.25GHz-27.5 GHz), e.g., 3GPP 5G n261 band 9052 (27.5 GHz-28.35 GHz), e.g.,3GPP 5G n257 band 9053 (26.5 GHz-29.5). A sixth application band 9060includes the 3GPP 5G n260 band 9060 (37 GHz-40 GHz). A seventhapplication band 9070 includes United States WiGig Band for IEEE802.11ad and IEEE 802.11ay 9071 (57 GHz-71 Ghz), European Union andJapan WiGig Band for IEEE 802.11ad and IEEE 802.11ay 9072 (57 GHz-66Ghz), South Korea WiGig Band for IEEE 802.11ad and IEEE 802.11ay 9073(57 GHz-64 Ghz), and China WiGig Band for IEEE 802.11ad and IEEE802.11ay 9074 (59 GHz-64 GHz). An eighth application band 9080 includesan automobile radar band 9080 (76 GHz-81 GHz).

Accordingly, it should be understood from the foregoing that theacoustic wave devices (e.g., resonators, filters and oscillators) ofthis disclosure may be implemented in the respective applicationfrequency bands just discussed. For example, the layer thicknesses ofthe acoustic reflector electrodes and piezoelectric layers inalternating axis arrangement for the example acoustic wave devices(e.g., the 5 GHz bulk acoustic wave resonators, e.g., the 24 GHz bulkacoustic wave resonators, e.g., the example 39 GHz bulk acoustic waveresonators) of this disclosure may be scaled up and down as needed to beimplemented in the respective application frequency bands justdiscussed. This is likewise applicable to the example filters (e.g.,bulk acoustic wave resonator based filters) and example oscillators(e.g., bulk acoustic wave resonator based oscillators) of thisdisclosure to be implemented in the respective application frequencybands just discussed. The following examples pertain to furtherembodiments for acoustic wave devices, including but not limited to,e.g., bulk acoustic wave resonators, e.g., bulk acoustic wave resonatorbased filters, e.g., bulk acoustic wave resonator based oscillators, andfrom which numerous permutations and configurations will be apparent. Afirst example is an acoustic wave device comprising first and secondlayers of piezoelectric material acoustically coupled with one anotherto have a piezoelectrically excitable resonance mode, in which the firstlayer of piezoelectric material has a first piezoelectric axisorientation, and the second layer of piezoelectric material has a secondpiezoelectric axis orientation that substantially opposes the firstpiezoelectric axis orientation of the first layer of piezoelectricmaterial, and in which the first and second layers of piezoelectricmaterial have respective thicknesses so that the acoustic wave devicehas a resonant. A second example is an acoustic wave device as describedin the first example, in which the resonant frequency of the acousticwave device is in a 3rd Generation Partnership Project (3GPP) band. Athird example is an acoustic wave device as described in the firstexample in which the resonant frequency of the acoustic wave device isin an Unlicensed National Information Infrastructure (UNII) band. Afourth example is an acoustic wave device as described in the firstexample, in which the resonant frequency of the acoustic wave device isin a 3GPP n77 band 9010 as shown in FIG. 9A. A fifth example is anacoustic wave device as described in the first example, in which theresonant frequency of the acoustic wave device is in a 3GPP n79 band9020 as shown in FIG. 9A. A sixth example is an acoustic wave device asdescribed in the first example, in which the resonant frequency of theacoustic wave device is in a 3GPP n258 band 9051 as shown in FIG. 9B. Aseventh example is an acoustic wave device as described in the firstexample, in which the resonant frequency of the acoustic wave device isin a 3GPP n261 band 9052 as shown in FIG. 9B. An eighth example is anacoustic wave device as described in the first example, in which theresonant frequency of the acoustic wave device is in a 3GPP n260 band asshown in FIG. 9B. A ninth example is an acoustic wave device asdescribed in the first example, in which the resonant frequency of theacoustic wave device is in an Institute of Electrical and ElectronicEngineers (IEEE) C band as shown in FIG. 9A. A tenth example is anacoustic wave device as described in the first example, in which theresonant frequency of the acoustic wave device is in an Institute ofElectrical and Electronic Engineers (IEEE) X band as shown in FIG. 9B.An eleventh example is an acoustic wave device as described in the firstexample, in which the resonant frequency of the acoustic wave device isin an Institute of Electrical and Electronic Engineers (IEEE) Ku band asshown in FIG. 9B. An twelfth example is an acoustic wave device asdescribed in the first example, in which the resonant frequency of theacoustic wave device is in an Institute of Electrical and ElectronicEngineers (IEEE) K band as shown in FIG. 9B. A thirteenth example is anacoustic wave device as described in the first example, in which theresonant frequency of the acoustic wave device is in an Institute ofElectrical and Electronic Engineers (IEEE) Ka band as shown in FIG. 9B.A fourteenth example is an acoustic wave device as described in thefirst example, in which the resonant frequency of the acoustic wavedevice is in an Institute of Electrical and Electronic Engineers (IEEE)V band as shown in FIG. 9B. A fifteenth example is an acoustic wavedevice as described in the first example, in which the resonantfrequency of the acoustic wave device is in an Institute of Electricaland Electronic Engineers (IEEE) W band as shown in FIG. 9B. A sixteenthexample is an acoustic wave device as described in the first example, inwhich the resonant frequency of the acoustic wave device is in UNII-1band 9031, as shown in FIG. 9A. A seventeenth example is an acousticwave device as described in the first example, in which the resonantfrequency of the acoustic wave device is in UNII-2A band 9032, as shownin FIG. 9A. A eighteenth example is an acoustic wave device as describedin the first example, in which the resonant frequency of the acousticwave device is in UNII-2C band 9041, as shown in FIG. 9A. A nineteenthexample is an acoustic wave device as described in the first example, inwhich the resonant frequency of the acoustic wave device is in UNII-3band 9042, as shown in FIG. 9A. A twentieth example is an acoustic wavedevice as described in the first example, in which the resonantfrequency of the acoustic wave device is in UNII-4 band 9043, as shownin FIG. 9A. A twenty first example is an acoustic wave device asdescribed in the first example, in which the resonant frequency of theacoustic wave device is in UNII-5 band 9044, as shown in FIG. 9A. Atwenty second example is an acoustic wave device as described in thefirst example, in which the resonant frequency of the acoustic wavedevice is in UNII-6 band 9045, as shown in FIG. 9A. A twenty thirdexample is an acoustic wave device as described in the first example, inwhich the resonant frequency of the acoustic wave device is in UNII-7band 9046, as shown in FIG. 9A. A twenty fourth example is an acousticwave device as described in the first example, in which the resonantfrequency of the acoustic wave device is in UNII-8 band 9047, as shownin FIG. 9A. A twenty fifth example is a bulk acoustic wave resonatorcomprising: a substrate; a first layer of piezoelectric material havinga first piezoelectric axis orientation; a second layer of piezoelectricmaterial acoustically coupled to the first layer of piezoelectricmaterial, the second layer of piezoelectric material having a secondpiezoelectric axis orientation that is antiparallel to the firstpiezoelectric axis orientation; and a first metal acoustic wavereflector electrically interfacing with the first layer of piezoelectricmaterial, the first metal acoustic wave reflector comprising a firstpair metal layers. A twenty sixth example is a bulk acoustic waveresonator as described in the twenty fifth example comprising a thirdlayer of piezoelectric material disposed between the first layer ofpiezoelectric material and the second layer of piezoelectric materialand being acoustically coupled to the first layer of piezoelectricmaterial and the second layer of piezoelectric material. A twentyseventh example is a bulk acoustic wave resonator as described in thetwenty sixth example comprising a fourth layer of piezoelectric materialdisposed between the first layer of piezoelectric material and thesecond layer of piezoelectric material and being acoustically coupled tothe first layer of piezoelectric material and the second layer ofpiezoelectric material and the third layer of piezoelectric material. Atwenty eighth example is a bulk acoustic wave resonator as described inthe twenty fifth example comprising a second metal acoustic wavereflector electrically interfacing with the second layer ofpiezoelectric material, the second metal acoustic wave reflectorcomprising a second pair metal layers.

FIGS. 9C and 9D are first and second diagrams 9100, 9200 illustratingrespective simulated bandpass characteristics 9101, 9201 of insertionloss versus frequency for example millimeter wave filters.

For example, FIG. 9C is a first diagram 9100 illustrating a firstsimulated bandpass characteristic 9101 of insertion loss versusfrequency for a first example millimeter wave filter configured as inFIG. 7 (e.g., inductors modifying an example lattice filter using afirst pair of series resonators of the bulk acoustic wave resonatorstructure of FIG. 1A, a second pair of series resonators of the bulkacoustic wave resonator structure of FIG. 1A and two pairs of crosscoupled mass loaded shunt resonators of the bulk acoustic wave resonatorstructure of FIG. 1A). For example, the first example millimeter wavefilter having the simulated bandpass characteristic 9101 may be a 3GPP5G n258 band filter (e.g., filter corresponding to the FIG. 9B 3GPP 5Gn258 band 9051 (24.25 GHz-27.5 GHz)). For example, the first examplemillimeter wave filter having the simulated bandpass characteristic 9101may have a fractional bandwidth of about twelve percent (12%), and mayinclude resonators having electromechanical coupling coefficient (Kt2)of about six and a half percent (6.5%). For example, the simulatedbandpass characteristic 9101 of FIG. 9C shows a first 3GPP 5G n258 bandedge feature 9103 having an insertion loss of −1.6328 decibels (dB) atan initial 24.25 GHz extremity of the 3GPP 5G n258 band. For example,the simulated bandpass characteristic 9101 of FIG. 9C shows an opposing3GPP 5G n258 band edge feature 9105 having an insertion loss of −1.648decibels (dB) at an opposing 27.5 GHz extremity of the 3GPP 5G n258band. The first example millimeter wave filter having the simulatedbandpass characteristic 9101 may have a pass band that is configured for3GPP 5G n258 applications. For example, the simulated bandpasscharacteristic 9101 of FIG. 9C shows a first 3GPP 5G n258 band roll offfeature 9107 having an insertion loss of −21.664 decibels (dB) at aninitial 23.56 GHz roll off extremity of the 3GPP 5G n258 band. At theinitial 23.56 GHz roll off extremity of the 3GPP 5G n258 band, the first3GPP 5G n258 band roll off feature 9107 may provide about twenty dB ofroll off at about 690 Mhz from the first 3GPP 5G n258 band edge feature9103 at the initial 24.25 GHz extremity of the 3GPP 5G n258 band. Forexample, the simulated bandpass characteristic 9101 FIG. 9C shows anopposing 3GPP 5G n258 band roll off feature 9109 having an insertionloss of −21.764 decibels (dB) at an opposing 28.02 GHz roll offextremity of the 3GPP 5G n258 band. At the opposing 28.02 GHz roll offextremity of the 3GPP 5G n258 band, the opposing 3GPP 5G n258 band rolloff feature 9109 may provide about twenty dB of roll off at about 580MHz from the opposing 3GPP 5G n258 band edge feature 9105 at theopposing 27.5 GHz extremity of the 3GPP 5G n258 band.

For example, FIG. 9D is a second diagram 9200 illustrating a secondsimulated bandpass characteristic 9201 of insertion loss versusfrequency for a second example millimeter wave filter configured as twoexternal shunt inductors modifying the example ladder filter of FIG. 6(e.g., an input port shunt inductor and an output port shunt inductormodifying the ladder configuration using five series resonators of thebulk acoustic wave resonator structure of FIG. 1A, and four mass loadedshunt resonators of the bulk acoustic wave resonator structure of FIG.1A). The shunt inductors may be, for example, 0.8 nanohenry inductorshaving a quality factor of twenty (Q of 20). For example, the secondexample millimeter wave filter having the simulated bandpasscharacteristic 9201 may be a 3GPP 5G n258 band channel filter (e.g.,filter corresponding to a channel in the FIG. 9B 3GPP 5G n258 band 9051(24.25 GHz-27.5 GHz)). For example, the second example millimeter wavefilter having the simulated bandpass characteristic 9201 may be a twohundred Megahertz (200 MHz) channel filter of the 3GPP 5G n258, e.g.,the filter may have a fractional bandwidth of about nine tenths of apercent (0.9%), and may include resonators having electromechanicalcoupling coefficient (Kt2) of about one and seven tenths percent (1.7%).For example, the simulated bandpass characteristic 9201 FIG. 9D shows afirst 3GPP 5G n258 band channel edge feature 9203 having an insertionloss of −2.9454 decibels (dB) at an initial 24.25 GHz channel extremityof the 3GPP 5G n258 band. For example, the simulated bandpasscharacteristic 9201 FIG. 9D shows an opposing 3GPP 5G n258 band channeledge feature 9205 having an insertion loss of −2.9794 decibels (dB) atan opposing 24.45 GHz extremity of the 3GPP 5G n258 band channel. Thesecond example millimeter wave filter having the simulated bandpasscharacteristic 9201 may have a channel pass band that is configured for3GPP 5G n258 applications. For example, the simulated bandpasscharacteristic 9201 of FIG. 9D shows a first 3GPP 5G n258 band channelroll off feature 9207 having an insertion loss of −22.406 decibels (dB)at an initial 24.203 GHz roll off extremity of the 3GPP 5G n258 bandchannel. At the initial 24.203 GHz roll off extremity of the 3GPP 5Gn258 band channel, the first 3GPP 5G n258 band channel roll off feature9207 may provide about twenty dB of roll off at about 50 Mhz from thefirst 3GPP 5G n258 band channel edge feature 9203 at the initial 24.25GHz extremity of the 3GPP 5G n258 band channel. For example, thesimulated bandpass characteristic 9201 FIG. 9D shows an opposing 3GPP 5Gn258 band channel roll off feature 9209 having an insertion loss of−22.291 decibels (dB) at an opposing 24.497 GHz channel roll offextremity of the 3GPP 5G n258 band channel. At the opposing 24.497 GHzchannel roll off extremity of the 3GPP 5G n258 band channel, theopposing 3GPP 5G n258 band roll off channel feature 9209 may provideabout twenty dB of roll off at about 50 Mhz from the opposing 3GPP 5Gn258 band channel edge feature 9205 at the opposing 24.45 GHz extremityof the 3GPP 5G n258 band channel.

FIG. 10 illustrates a computing system implemented with integratedcircuit structures or devices formed using the techniques disclosedherein, in accordance with an embodiment of the present disclosure. Asmay be seen, the computing system 1000 houses a motherboard 1002. Themotherboard 1002 may include a number of components, including, but notlimited to, a processor 1004 and at least one communication chip 1006A,1006B each of which may be physically and electrically coupled to themotherboard 1002, or otherwise integrated therein. As will beappreciated, the motherboard 1002 may be, for example, any printedcircuit board, whether a main board, a daughterboard mounted on a mainboard, or the only board of system 1000, etc.

Depending on its applications, computing system 1000 may include one ormore other components that may or may not be physically and electricallycoupled to the motherboard 1002. These other components may include, butare not limited to, volatile memory (e.g., DRAM), non-volatile memory(e.g., ROM), a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth). Any of the components included in computingsystem 1000 may include one or more integrated circuit structures ordevices formed using the disclosed techniques in accordance with anexample embodiment. In some embodiments, multiple functions may beintegrated into one or more chips (e.g., for instance, note that thecommunication chips 1006A, 1006B may be part of or otherwise integratedinto the processor 1004).

The communication chips 1006A, 1006B enables wireless communications forthe transfer of data to and from the computing system 1000. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chips 1006A may implementany of a number of wireless standards or protocols, including, but notlimited to, Wi-Fi (IEEE 802.1 1 family), WiMAX (IEEE 802.16 family),IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+,EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, aswell as any other wireless protocols that are designated as 3G, 4G, 5G,and beyond. The computing system 1000 may include a plurality ofcommunication chips 1006A, 1006B. For instance, a first communicationchip 1006A may be dedicated to shorter range wireless communicationssuch as Wi-Fi and Bluetooth and a second communication chip 1006B may bededicated to longer range wireless communications such as GPS, EDGE,GPRS, CDMA, WiMAX, LTE, Ev-DO, 5G and others. In some embodiments,communication chips 1006A, 1006B may include one or more acoustic wavedevices 1008A, 1008B (e.g., resonators, filters and/or oscillators1008A, 1008B) as variously described herein (e.g., acoustic wave devicesincluding a stack of alternating axis piezoelectric material). Acousticwave devices 1008A, 1008B may be included in various ways, e.g., one ormore resonators, e.g., one or more filters, e.g., one or moreoscillators. Further, such acoustic wave devices 1008A, 1008B, e.g.,resonators, e.g., filters, e.g., oscillators may be configured to beSuper High Frequency (SHF) acoustic wave devices 1008A, 1008B orExtremely High Frequency (EHF) acoustic wave devices 1008A, 1008B, e.g.,resonators, filters, and/or oscillators (e.g., operating at greater than3, 4, 5, 6, 7, or 8 GHz, e.g., operating at greater than 23, 24, 25, 26,27, 28, 29, or 30 GHz, e.g., operating at greater than 36, 37, 38, 39,or 40 GHz). Further still, such Super High Frequency (SHF) acoustic wavedevices or Extremely High Frequency (EHF) resonators, filters, and/oroscillators may be included in the RF front end of computing system 1000and they may be used for 5G wireless standards or protocols, forexample.

The processor 1004 of the computing system 1000 includes an integratedcircuit die packaged within the processor 1004. In some embodiments, theintegrated circuit die of the processor includes onboard circuitry thatis implemented with one or more integrated circuit structures or devicesformed using the disclosed techniques, as variously described herein.The term “processor” may refer to any device or portion of a device thatprocesses, for instance, electronic data from registers and/or memory totransform that electronic data into other electronic data that may bestored in registers and/or memory.

The communication chips 1006A, 1006B also may include an integratedcircuit die packaged within the communication chips 1006A, 1006B. Inaccordance with some such example embodiments, the integrated circuitdie of the communication chip includes one or more integrated circuitstructures or devices formed using the disclosed techniques as variouslydescribed herein. As will be appreciated in light of this disclosure,note that multi-standard wireless capability may be integrated directlyinto the processor 1004 (e.g., where functionality of any chips 1006A,1006B is integrated into processor 1004, rather than having separatecommunication chips). Further note that processor 1004 may be a chip sethaving such wireless capability. In short, any number of processor 1004and/or communication chips 1006A, 1006B may be used. Likewise, any onechip or chip set may have multiple functions integrated therein.

In various implementations, the computing device 1000 may be a laptop, anetbook, a notebook, a smartphone, a tablet, a personal digitalassistant (PDA), an ultra-mobile PC, a mobile phone, a desktop computer,a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player, adigital video recorder, or any other electronic device that processesdata or employs one or more integrated circuit structures or devicesformed using the disclosed techniques, as variously described herein.

Further Example Embodiments

The following examples pertain to further embodiments, from whichnumerous permutations and configurations will be apparent. The foregoingdescription of example embodiments has been presented for the purposesof illustration and description. It is not intended to be exhaustive orto limit the present disclosure to the precise forms disclosed. Manymodifications and variations are possible in light of this disclosure.It is intended that the scope of the present disclosure be limited notby this detailed description, but rather by the claims appended hereto.Future filed applications claiming priority to this application mayclaim the disclosed subject matter in a different manner, and maygenerally include any set of one or more limitations as variouslydisclosed or otherwise demonstrated herein.

What is claimed is:
 1. An electrical ladder filter comprising: aplurality of bulk acoustic wave (BAW) resonators, the plurality of BAWresonators being electrically coupled to facilitate the electricalladder filter; the plurality of BAW resonators comprising a first BAWresonator comprising: a top multilayer acoustic reflector electrode; abottom multilayer acoustic reflector electrode; and a stack comprising atriplet of piezoelectric layers between the top multilayer acousticreflector electrode and the bottom multilayer acoustic reflectorelectrode, and having a piezoelectrically excitable resonance mode, inwhich the top multilayer acoustic reflector electrode comprises atriplet of top metal electrode layers electrically and acousticallycoupled with the triplet of piezoelectric layers to facilitate excitingthe piezoelectrically excitable resonance mode at a main resonantfrequency associated with the stack comprising the triplet ofpiezoelectric layers, and in which the main resonant frequencyassociated with the stack comprising the triplet of piezoelectric layersis in one of a Ku band, a K band, a Ka band, a V band, and a W band, asassociated with an Institute of Electrical and Electronic Engineers(IEEE).
 2. The electrical ladder filter as in claim 1 in which thebottom multilayer acoustic reflector electrode comprises a triplet ofbottom metal electrode layers electrically and acoustically coupled withthe triplet of piezoelectric layers to facilitate exciting thepiezoelectrically excitable resonance mode at the main resonantfrequency.
 3. The electrical ladder filter as in claim 2 in which thetriplet of top metal electrode layers comprises a middle metal memberhaving a middle acoustic impedance between a pair of metal membershaving acoustic impedances that are substantially different than themiddle acoustic impedance of the middle metal member.
 4. The electricalladder filter as in claim 1 in which: the first BAW resonator comprisesfourth and fifth piezoelectric layers; and the fourth and fifthpiezoelectric layers have the piezoelectrically excitable resonance modewith the triplet of piezoelectric layers; the fourth piezoelectric layerhas a fourth piezoelectric axis orientation; and the fifth piezoelectriclayer has a piezoelectric axis orientation that substantially opposesthe fourth piezoelectric axis orientation of the fourth piezoelectriclayer.
 5. An electrical oscillator comprising: active gain circuitry;and a bulk acoustic wave resonator comprising: a top multilayer acousticreflector electrode; and a stack comprising first, second, third, fourthand fifth piezoelectric layers acoustically coupled to have apiezoelectrically excitable resonance mode, in which the firstpiezoelectric layer has a first piezoelectric axis orientation, and thesecond piezoelectric layer has a second piezoelectric axis orientationthat substantially opposes the first piezoelectric axis orientation ofthe first piezoelectric layer, in which the top multilayer acousticreflector electrode comprises a triplet of top metal electrode layerselectrically coupled with the first, second, third, fourth and fifthpiezoelectric layers and with the active gain circuitry to facilitateexciting a piezoelectrically excitable resonance mode at a main resonantfrequency in one of a Ku band, a K band, a Ka band, a V band, and a Wband, as associated with an Institute of Electrical and ElectronicEngineers (IEEE), and in which the first, second, third, fourth andfifth piezoelectric layers of the stack are free of any interposingelectrode.
 6. The electrical oscillator as in claim 5 in which: theactive gain circuitry comprises a transistor; and the bulk acoustic waveresonator comprises a bottom multilayer acoustic reflector electrodecomprising a triplet of bottom metal electrode layers electrically andacoustically coupled with the first, second, third, fourth and fifthpiezoelectric layers to facilitate exciting the piezoelectricallyexcitable resonance mode.
 7. An apparatus comprising: a bulk acousticwave resonator comprising: a substrate; a stack comprising first, secondand third piezoelectric layers acoustically coupled to have apiezoelectrically excitable resonance mode, in which the firstpiezoelectric layer has a first piezoelectric axis orientation, and thesecond piezoelectric layer has a second piezoelectric axis orientationthat substantially opposes the first piezoelectric axis orientation ofthe first piezoelectric layer, and in which the first, second and thirdpiezoelectric layers have respective thicknesses to facilitate the bulkacoustic wave resonator having a main resonant frequency in one of a Kuband, a K band, a Ka band, a V band, and a W band; and a top multilayeracoustic reflector electrode comprising a triplet of top metal electrodelayers electrically and acoustically coupled with the first, second andthird piezoelectric layers to excite the piezoelectrically excitableresonance mode at the main resonant frequency.
 8. The apparatus as inclaim 7 in which the bulk acoustic wave resonator comprises a bottommultilayer acoustic reflector electrode.
 9. The apparatus as in claim 8in which a first mesa structure of the bulk acoustic wave resonatorcomprises the first, second and third piezoelectric layers, a secondmesa structure of the bulk acoustic wave resonator comprises the bottommultilayer acoustic reflector electrode, and a third mesa structure ofthe bulk acoustic wave resonator comprises the top multilayer acousticreflector electrode.
 10. The apparatus as in claim 8 in which the bottommultilayer acoustic reflector electrode comprises a triplet of bottommetal electrode layers electrically and acoustically coupled with thefirst, second and third piezoelectric layers to excite thepiezoelectrically excitable resonance mode at the main resonantfrequency.
 11. The apparatus as in claim 7 in which: the top multilayeracoustic reflector electrode comprises a connection portion of the topmultilayer acoustic reflector electrode; and a gap is formed beneath theconnection portion of the top multilayer acoustic reflector electrodeadjacent to an etched edge region extending through the first, secondand third piezoelectric layers; and the gap is filled with air or adielectric material.
 12. The apparatus as in claim 11 in which: the bulkacoustic wave resonator comprises a bottom multilayer acoustic reflectorelectrode; and the etched edge region extends through the bottommultilayer acoustic reflector electrode, through the first, second andthird piezoelectric layers, to the connection portion of the topmultilayer acoustic reflector electrode.
 13. The apparatus as in claim 7in which: the top multilayer acoustic reflector electrode comprises asecond triplet of top metal electrode layers electrically andacoustically coupled with the third piezoelectric layer to excite thepiezoelectrically excitable resonance mode at the main resonantfrequency; and members of the triplet of top metal electrode layers andthe second triplet of top metal electrode layers have respectiveacoustic impedances in an alternating arrangement to provide a pluralityof reflective acoustic impedance mismatches.
 14. The apparatus as inclaim 7 comprising at least one or more of: fourth and fifthpiezoelectric layers arranged over the first, second and thirdpiezoelectric layers; a third pair of piezoelectric layers; a fourthpair of piezoelectric layers; a sixth pair of piezoelectric layers; aseventh pair of piezoelectric layers; and an eighth pair ofpiezoelectric layers, in which at least one pair of piezoelectric layershave respective piezoelectric axis orientations that are substantiallyopposing.
 15. The apparatus as in claim 7 in which the top multilayeracoustic reflector electrode has thermal resistance of three thousanddegrees Kelvin per Watt or less at the main resonant frequency of thebulk acoustic wave resonator.
 16. The apparatus as in claim 7 in whichthe bulk acoustic wave resonator has a quality factor of approximately730 or greater.
 17. The apparatus as in claim 7 in which the topmultilayer acoustic reflector electrode has sheet resistance of lessthan one Ohm per square at the main resonant frequency of the bulkacoustic wave resonator.
 18. The apparatus as in claim 7 in which themain resonant frequency of the bulk acoustic wave resonator is in the Kaband, as associated with an Institute of Electrical and ElectronicEngineers (IEEE).
 19. The apparatus as in claim 7 in which the mainresonant frequency of the bulk acoustic wave resonator is in a 3rdGeneration Partnership Project (3GPP) band.
 20. The apparatus as inclaim 7 in which the main resonant frequency of the bulk acoustic waveresonator is in at least one of a 3GPP n257 band, a 3GPP n258 band, a3GPP n260 band, and a 3GPP n261 band.
 21. The apparatus as in claim 7 inwhich a peak acoustic reflectivity of the top multilayer acousticreflector electrode is in one of the Ku band, the K band, the Ka band,the V band, and the W band.
 22. The apparatus as in claim 7 in which themain resonant frequency of the bulk acoustic wave resonator is in a 3GPPn258 band, as associated with a 3rd Generation Partnership Project(3GPP).
 23. An acoustic wave device, comprising: a top multilayer metalacoustic wave reflector; a bottom multilayer metal acoustic wavereflector; and a stack between the top multilayer metal acoustic wavereflector and the bottom multilayer metal acoustic wave reflector, thestack comprising a plurality of piezoelectric layers having respectivethicknesses, the respective thicknesses to facilitate a main acousticresonance frequency of the acoustic wave device in one of a Ku band, a Kband, a Ka band, a V band, and a W band, the plurality of piezoelectriclayers comprising first, second, third, fourth and fifth piezoelectriclayers, in which: the top multilayer metal acoustic wave reflectorcomprises a triplet of top metal layers electrically interfacing withthe fifth piezoelectric layer; the bottom multilayer metal acoustic wavereflector comprises a plurality of bottom metal layers electricallyinterfacing with the first piezoelectric layer; and the plurality ofpiezoelectric layers of the stack is free of any interposing electrode.24. The acoustic wave device of claim 23 in which the acoustic wavedevice has a quality factor of approximately 730 or greater.
 25. Aresonator ladder filter comprising: a plurality of acoustic waveresonator devices electrically coupled to facilitate the resonatorladder filter, in which the plurality of acoustic wave resonator devicescomprises a first acoustic wave resonator device comprising: a topmultilayer metal acoustic wave reflector; a bottom multilayer metalacoustic wave reflector; and a stack between the top multilayer metalacoustic wave reflector and the bottom multilayer metal acoustic wavereflector, the stack comprising a plurality of piezoelectric layers, theplurality of piezoelectric layers having respective thicknesses, therespective thicknesses to facilitate a main acoustic resonance frequencyof the first acoustic wave device in one of a Ku band, a K band, a Kaband, a V band, and a W band, the plurality of piezoelectric layerscomprising first, second, third, fourth and fifth piezoelectric layers,in which: the top multilayer metal acoustic wave reflector comprises atriplet of top metal layers electrically interfacing with the fifthpiezoelectric layer; the bottom multilayer metal acoustic wave reflectorcomprises a plurality of metal layers electrically interfacing with thefirst piezoelectric layer; and the plurality of piezoelectric layers ofthe stack is free of any interposing electrode.
 26. The resonator ladderfilter of claim 25 in which the main acoustic resonance frequency of thefirst acoustic wave device is in the K band, as associated with anInstitute of Electrical and Electronic Engineers (IEEE).
 27. Theresonator ladder filter of claim 25 in which the main acoustic resonancefrequency of the first acoustic wave device is in at least one of a 3GPPn257 band, a 3GPP n258 band, a 3GPP n260 band, and a 3GPP n261 band. 28.An apparatus comprising: a bulk acoustic wave resonator comprising: asubstrate; a first piezoelectric layer having a first piezoelectric axisorientation; a second piezoelectric layer acoustically coupled to thefirst piezoelectric layer, the second piezoelectric layer having asecond piezoelectric axis orientation that substantially opposes thefirst piezoelectric axis orientation; a third, fourth and fifthpiezoelectric layer; and a first multilayer metal acoustic wavereflector comprising a first triplet of metal layers electricallyinterfacing with the fifth piezoelectric layer to facilitate exciting amain resonant frequency in one of a Ku band, a K band, a Ka band, a Vband, and a W band.
 29. The apparatus of claim 28 in which the bulkacoustic wave resonator comprises a sixth piezoelectric layer.
 30. Theapparatus of claim 28 in which the bulk acoustic wave resonatorcomprises a second multilayer metal acoustic wave reflector electricallyinterfacing with the sixth piezoelectric layer, the second multilayermetal acoustic wave reflector comprising a second triplet of metallayers.